Japan's nuclear crisis

Following are main developments after a massive earthquake and tsunami devastated northeast Japan and crippled a nuclear power station, raising the risk of uncontrolled radiation.

* Japan's nuclear safety agency says military will help pump water at the No.3 reactor at the quake-damaged Fukushima Daiichi nuclear power complex in northeastern Japan, and into the spent fuel pool in No.4 reactor.

- Agency also says radiation levels outside the plant spiked around noon but fell back.

- A helicopter was unable to drop water to cool the No.3 reactor, probably because of the high radiation, Kyodo news agency said, quoting the defense minister.

- Police will attempt to cool No.4 reactor's spent nuclear fuel pool using a water cannon, NHK TV says.

- Japan's top government spokesman says radiation levels around the complex are not at levels to cause an immediate health risk.

- Tokyo is safe for international travelers, the Japanese Red Cross says.

- There is no evidence of a significant spread of radiation from Japan's crippled nuclear plants, the World Health Organization says.

- Operator says it is unable to resume work cooling the reactors due to radiation risk. Workers ordered to leave the plant were allowed back in after radiation levels fall. Operator says there were 180 workers on site as of 0230 GMT.

- Fire breaks out at reactor No.4 a day after a blast blew a hole in the building housing spent fuel rods. White smoke seen from No.3 reactor most likely to be steam from the water that is being poured to cool the rods.

- No plan yet to extend evacuation zone near the facility, 240 km (150 miles) north of Tokyo.

- Australia urges its citizens with non-essential roles to consider leaving Tokyo and the most damaged prefectures, and Turkey warns citizens against traveling to Japan. France urges nationals living in Tokyo to leave country or move south.

- Radiation levels in Tokyo were 10 times normal at one point, but not a threat to human health, officials said.

- Japan's benchmark Nikkei average closes 4.5 percent up on Wednesday after suffering its worst two-day rout since 1987. The index surged over 6 percent at one point.

- Tens of thousands of people are still missing since Friday's quake and tsunami. About 850,000 households in the north without electricity in near-freezing weather. Death toll is expected to exceed 10,000.