(Reuters)- Japan is under global scrutiny over the handling of its nuclear crisis after a huge earthquake crippled several reactors at a nuclear power complex, raising fears of an uncontrolled radiation leak.

Below is a timeline of statements made by Japanese authorities and the complex's owner, Tokyo Electric Power (TEPCO), after the quake struck on Friday, the strongest tremor ever recorded in Japan.

(Times are Japan time, which is GMT +9, unless stated)

THURSDAY, MARCH 17

02:58 - Britain advises its citizens in Japan to consider leaving Tokyo and the area north of the capital.

WEDNESDAY, MARCH 16

21:48 - Japan wants to use its military to help pump water to the No.3 reactor and into a spent-fuel pool at the No.4 reactor of a quake-stricken nuclear plant, the nation's nuclear safety agency says.

Radiation levels at a monitoring post outside the Fukushima Daiichi plant had spiked at 0330 GMT to 10,850 microsieverts per hour, but fell back later to 2,331 microsieverts an hour later, it says.

21:01 - Major damage is unlikely to have been sustained at the No.3 reactor of Japan's quake-stricken nuclear power plant, Kyodo reports, quoting the government.

19:53 - Japanese police will attempt to cool the spent nuclear fuel pool at the No. 4 reactor at the stricken Fukushima Daiichi nuclear plant using a water cannon truck as early as Wednesday night, NHK television says.

19:47 - No radioactive iodine or cesium was found in the tap water of Japan's Fukushima prefecture, Kyodo news agency reports, quoting the local government.

18:29 - Water is being poured into reactors No.5 and No.6 at Fukushima's Daiichi nuclear power plant, the operating company says.

18:14 - A helicopter was unable to drop water to cool a quake-stricken reactor in northeastern Japan probably because of the high radiation, Kyodo news agency says, quoting the defense minister.

18:00 - Japan's top government spokesman says radiation levels around the nuclear plant are not at levels to cause an immediate health risk.

17:32 - The World Health Organisation's representative in China says there is no evidence of any significant international spread of radiation from the nuclear site.

17:26 - The operator of Japan's quake-stricken nuclear power complex, Tokyo Electric Power Co Ltd, says it is unable to resume work on cooling reactors due to radiation risk.

16:55 - Operator says as of 0230 GMT there were 180 workers on site at the damaged nuclear power complex.

16:55 - Tokyo Electric Power Co says it recorded the site's highest levels of radiation at the No.3 reactor on Wednesday.

16:05 - The temperature stabilized and pressure dropped at the No. 2 reactor, the plant operator said.

13:27 - Japan's nuclear safety agency says operators of the damaged nuclear plant plan to bulldoze an emergency route to the facility to allow access for fire trucks.

11:38 - Japan may seek direct U.S. military help to end the crisis at the plant, the chief government spokesman says.

11:30 - It is not realistic to think that the No. 4 reactor at the plant will "reach criticality", the chief government spokesman says.

11:19 - The radiation reading at the main gate of the plant rose sharply just after 0100 GMT on Friday and started to fall almost an hour later, the government says.

11:10 - A fuel pool at the No.3 reactor at the Fukushima Daiichi plant may have heated and produced steam, TEPCO says. Media images earlier showed white smoke drifting from the plant.

11:38 - Japan may seek direct U.S. military help to end the crisis at the plant, the chief government spokesman says.

TUESDAY, MARCH 15

20:54 - Radiation levels at the No. 4 reactor of the Fukushima Daiichi nuclear-power plant has become too high to conduct normal work from its control room, Kyodo news agency says. Workers cannot stay long and are going in and out of the control room as well as monitoring from a different place.

20:50 - The radiation level in the Japanese capital, Tokyo, is 10 times normal, but there is no threat to human health, the city government says.

19:09 - Winds are now dispersing radioactive material from the Japanese nuclear crisis over the Pacific Ocean, away from Japan and other Asian countries, the World Meteorological Organization (WMO) says.

18:20 - Japan's nuclear safety agency says there are two holes of 8-metres square in a wall of the outer building of the quake-hit Fukushima Daiichi No.4 reactor after a blast in the morning.

18:06 - Radiation levels in Chiba prefecture, near Tokyo, are more than 10 times above normal levels, Kyodo reports.

18:01: TEPCO has pulled out 750 workers from the plant since Tuesday, and 50 remain, it says.

17:48 - A pool containing spent fuel at the No.4 reactor may be boiling and the water level may be falling, Kyodo news agency quoted an official at the reactor's operator as saying.

17:31 - Japan has told the U.N. Agency radioactivity was being released "directly" into the atmosphere, the IAEA says.

17:28 - Radiation levels fall at the plant, the government says. Chief Cabinet Secretary Yukio Edano says the radiation level at the main gate of the Fukushima Daiichi complex is 596.4 microsieverts per hour as of 0630 GMT, down from 11,930 microsieverts at 0000 GMT.

16:44 - Japan has told the United Nations nuclear watchdog (IAEA) that it has extinguished a fire at the spent fuel storage pond at the power plant, the Vienna-based agency says.

14:46 - Radiation levels in the city of Maebashi, 100 km north of Tokyo, are up to 10 times normal, Kyodo says, quoting the city government.

14:07 - A no-fly zone is established for a 30-km radius around the plant, Jiji news agency says, quoting the transport ministry.

14:03 - Prime Minister Kan sends a text message to mobile phone users across the country, asking them to conserve power.

14:00 - Radiation levels in Tokyo are "not a problem", the city government says.

12:37 - Minute levels of radiation have been detected in Tokyo, Kyodo says, quoting local government.

12:03 - Winds over the plant are blowing in a southwesterly direction that includes Tokyo, but will shift later on Tuesday, the weather agency says.

11:57 - Japan's science minister has asked local governments to make more frequent radiation checks, Kyodo news agency says.

The agency also says there has been one explosion at the No. 4 reactor at a stricken plant.

11:08 - Risk of a nuclear leakage is rising, Prime Minister Naoto Kan says, and warns people within a 30-km radius to stay indoors.

11:41 - Radiation levels in Kanagawa prefecture, west of Tokyo, are up to nine times the normal level briefly on Tuesday, Kyodo news agency says, quoting the prefecture government.

11:08 - Risk of a nuclear leakage is rising, Prime Minister Naoto Kan says, and warns people within a 30-km radius to stay indoors.

10:03 - The nuclear safety agency says it is unsure if the explosion at the reactor has damaged one of its reactor containment vessels. If the containment vessel were to break and fuel rods within it to melt, it could cause a major radiation leak.

09:01 - Radiation levels in the air surrounding the plant have risen fourfold after the explosion, plant operator TEPCO says.

08:45 - The roof above overheating No. 2 reactor is damaged and steam in rising from the complex, Jiji news agency reports.

07:57 - Fresh explosion heard at the plant, Japan's nuclear safety agency says.

06:45 - Some damage has been detected at Fukushima Daiichi No. 2 reactor, but no sharp increase in radiation levels has been seen, Chief Cabinet Secretary Yukio Edano says.

MONDAY, MARCH 14

20:10 - Water levels inside the Fukushima Daiichi complex's No. 2 reactor are almost empty, TEPCO says. Jiji news agency says the operator of the plant has started injecting sea water to the reactor in the hope of cooling it down.

19:52 - Jiji quotes TEPCO as saying nuclear fuel rods at the Fukushima Daiichi complex's No.2 reactor, where levels of water coolant around the reactor core had been reported as falling earlier in the day, are now fully exposed. Jiji says a meltdown of the fuel rods cannot be ruled out.

17:23 - Jiji news agency says Japanese authorities have safely cooled down two nuclear reactors at the Fukushima Daini nuclear plant, close to another nuclear complex where they are still struggling to cool three overheating reactors.

16:17 - Chief Cabinet Secretary Yukio Edano confirms water levels at the Fukushima Daiichi plant No.2 reactor are falling and its cooling functions have stopped.

15:26 - The IAEA says Japan has told the U.N. nuclear watchdog the hydrogen explosion at the No.3 reactor at Fukushima Daiichi did not damage the primary containment vessel.

15:17 - Jiji news agency reports that there has been an explosion at a fuel oil tank at a thermal power plant in Fukushima and that the tank is on fire. It is not immediately clear which company the thermal power plant belonged to.

12:43 - Chief Cabinet Secretary Yukio Edano says a large-scale radiation leakage is unlikely from the Fukushima Daiichi plant's No. 3 reactor hit by an explosion after cooling problems.

11:40 - Jiji quotes TEPCO as saying a fresh explosion that rocked Fukushima Daiichi has not damaged the plant's No.3 reactor vessel.

11:20 - Japan's nuclear safety agency confirms a new explosion rocked the Fukushima Daiichi nuclear power complex, sending a plume of smoke into the air. But it says it cannot confirm whether or not the hydrogen explosion at the plant's No. 3 reactor has led to an uncontrolled leak of radioactivity.

11:11 - Domestic media image shows smoke rising from the No.3 reactor at Japan's Fukushima Daiichi nuclear plant. Japanese TV says there was a hydrogen explosion at the plant.

07:29 - TEPCO says it has reported a rise in radiation levels at its Fukushima Daiichi nuclear power plant to the government.

01:43 - Japan Atomic Power says the cooling process is working at its Tokai No. 2 nuclear power plant's reactor although two of the three diesel power generators used for cooling are out of order. The reactor at the plant, about 120 km (75 miles) north of Tokyo in Ibaraki prefecture, was automatically shut after Friday's earthquake and tsunami.

SUNDAY, MARCH 13

23:37 - Jiji quotes TEPCO as saying it is preparing to put sea water into the No.2 reactor at its Fukushima Daiichi nuclear power plant. The company is already injecting sea water into the No. 1 and No. 3 units at the plant to cool them down and reduce pressure inside reactor container vessels.

15:23 - Chief Cabinet Secretary Edano says there is a risk of an explosion at a building housing at the Fukushima Daiichi complex where an explosion on Saturday blew off the roof off another reactor building.

10:38 - Kyodo quotes TEPCO as saying radiation levels have risen above safe limits around the complex and that the firm has informed the government of an "emergency situation". It did not mean an immediate threat to human health, TEPCO says.

06:20 - The number of individuals exposed to radiation from the Fukushima Daiichi complex could reach as high as 160, an official of the Japan Nuclear and Industrial Safety Agency.

05:41 - In a 20-km radius around the Fukushima Daiichi complex, an estimated 110,000 people have been evacuated, the IAEA says. In a 10-km radius around the nearby Fukushima Daini complex, about 30,000 people have been evacuated.

00:49 - A nuclear accident in Japan on Saturday rates as less serious than both the Three Mile Island accident in 1979 and the 1986 Chernobyl nuclear disaster, Japan's nuclear safety agency said. An official at the agency said it has rated the incident at 4 under the International Nuclear and Radiological Event Scale. Three Mile Island was rated 5 while Chernobyl was rated 7 on the 1 to 7 scale, the official said.

SATURDAY, MARCH 12

22:21 - The IAEA quotes Japanese authorities as saying they are preparing to distribute iodine to people living near the stricken nuclear power complex. Iodine can be used to help protect the body from radioactive poisoning.

20:43 - TEPCO plans to fill the leaking reactor with sea water to cool it and reduce pressure in the unit, Edano says.

"The nuclear reactor is surrounded by a steel reactor container, which is then surrounded by a concrete building," Edano says. "The concrete building collapsed. We found out that the reactor container inside didn't explode."

"We've confirmed that the reactor container was not damaged. The explosion didn't occur inside the reactor container. As such there was no large amount of radiation leakage outside," he adds.

"At this point, there has been no major change to the level of radiation leakage outside (from before and after the explosion), so we'd like everyone to respond calmly."

"We've decided to fill the reactor container with sea water. Trade Minister Kaieda has instructed us to do so. By doing this, we will use boric acid to prevent criticality."

Edano says it will take about five to 10 hours to fill the reactor core with sea water and around 10 days to complete the process. He says due to the falling cooling-water level, hydrogen was generated and leaked into a space between the building and the container. It mixed with oxygen and exploded.

17:47 - Cabinet Secretary Edano confirms an explosion and radiation leak at Fukushima Daiichi. "We are looking into the cause and the situation and we'll make that public when we have further information," Edano says. "At present, we think 10 km evacuation is appropriate."

10:07 - TEPCO has begun releasing pressure from No. 1 reactor at Fukushima Daiichi nuclear plant, the Trade Ministry says. TEPCO says it will prepare for the release of pressure from the second nuclear plant, the Fukushima Daini plant, as pressure mounts. TEPCO and the authorities battle to contain rising pressure at the plants. They say thousands of residents in the area have been evacuated.

09:34 - Kyodo news agency says Japan has begun evacuating about 20,000 people from vicinity of the nuclear plants.

07:19 - TEPCO says it has lost its ability to control pressure in some reactors of a second nuclear power plant at its Fukushima facility. Pressure is stable inside the reactors but rising in the containment vessels, a spokesman says, although he did not know if there would be a need to release pressure at the plant at this point, which would involve a release of radiation.

06:37 - U.S. officials say the U.S. military did not provide any coolant for the Japanese nuclear plant, despite Clinton's earlier remarks. They say U.S. Air Force "assets" in Japan delivered coolant to a nuclear plant. One U.S. official says Japan had asked the United States for the coolant but ultimately handled the matter on its own.

03:14 - Cabinet Secretary Edano says TEPCO realizes the need to release pressure inside the plant, that this could cause a small radiation leak.

03:13 - Kyodo news agency quotes Japan's trade minister as saying a radiation leak could take place at the plant.

03:04 - Japan's nuclear safety watchdog confirms TEPCO is considering steps to lower the pressure in a container in the No. 1 reactor. A spokesman for the Nuclear and Industrial Safety Agency says it is unknown whether radiation levels are high in the container, which is inside a turbine building.

02:00 - Kyodo news agency quotes TEPCO as saying pressure inside the No. 1 reactor rose to 1.5 times designed capacity.

01:46 - Jiji quotes TEPCO as saying pressure inside the No. 1 reactor at the plant has been rising, with the risk of a radiation leak. It plans to take measures to release the pressure, the report says.

01:27 - Jiji says Fukushima prefecture expects cooling function at the plant to be restored by 1630 GMT (0130 local)

00:40 - U.S. Secretary of State Hillary Clinton says the United States has transported coolant to the stricken nuclear plant. "We just had our Air Force assets in Japan transport some really important coolant to one of the nuclear plants," Clinton says at a meeting of the President's Export Council.

00:38 - The World Nuclear Association, the main nuclear industry body, says it understands the situation is under control, and water is being pumped into the reactor's cooling system. An analyst at the association says he understood a back-up battery power system had been brought online after about an hour, and begun pumping water back into the cooling system.

FRIDAY, MARCH 11

22:45 - Vienna-based International Atomic Energy Agency (IAEA) says Japan advised that a heightened state of alert has been declared but no release of radiation had been detected.

It says Japanese authorities also reported a fire at the Onagawa nuclear power plant, which has since been extinguished.

"They say Onagawa, Fukushima Daini and Tokai nuclear power plants were also shut down automatically, and no radiation release has been detected," the statement says.

21:55 - The government says radiation has leaked from one of the plant's reactors.

21:49 - Jiji news agency says evacuation area around the plant is extended to 3 km from 2 km and quotes authorities as saying no radioactive leak has been confirmed.

21:34 - TEPCO confirms water levels falling inside reactors at the plant, and says it is trying to avert the exposure of nuclear fuel rods by restoring power to its emergency power system so that it can pump water inside the reactors.

19:46 - The government reveals a cooling problem at TEPCO's Fukushima Daiichi nuclear plant on the northeast coast, which bore the brunt of the quake and tsunami. Chief Cabinet Secretary Yukio Edano says the government has declared an emergency as a precaution but he says there is no radioactive leak.