New fire at Fukushima nuclear plant
Fire has again broken out at the quake-stricken Fukushima Daiichi nuclear plant in northern Japan.
The blaze has struck reactor four, where spent fuel rods are kept. The plant has already been hit by four explosions, triggering radiation leaks and sparking health concerns.
Friday's 9.0-magnitude earthquake damaged the plant's cooling functions.
More than 3,000 have been confirmed dead and thousands are missing after the quake and tsunami last Friday.
Officials have warned people within 20-30km (12-19 miles) of the site to either leave the area or stay indoors.
The crisis at the plant - which contains six nuclear reactors - has worsened since the earthquake struck. Explosions rocked the buildings housing reactors one and three on Saturday and Monday.
On Tuesday morning, a third blast hit the building of reactor two, while a fourth damaged the building of reactor four, where a fire also broke out in the unit's spent fuel storage pond.
Reactor four had been shut down before the quake for maintenance, but its spent nuclear fuel rods were still stored on the site.
Officials said the explosions at the first three reactors, and possibly the fourth as well, were caused by a buildup of hydrogen.
Chief Cabinet Secretary Yukio Edano said officials were closely watching the remaining two reactors, as they had begun overheating slightly.
He said cooling seawater was being pumped into reactors one and three - which were returning to normal - and into reactor two, which remained unstable.
Japan's nuclear safety agency said earlier it suspected the blast may have damaged reactor two's suppression chamber, which would have allowed radioactive steam to escape.
Health hazardAfter Tuesday's explosions and fire, radiation dosages of up to 400 millisieverts per hour were recorded at the Fukushima Daiichi site, about 250km north-east of Tokyo.
A single dose of 1,000 millisieverts causes temporary radiation sickness such as nausea and vomiting.
Later, a reading of 0.6 millisieverts (mSv) per hour was made at the plant's main gate, the International Atomic Energy Agency (IAEA) said.
The repeated releases of different amounts of radiation - some large, some small - are unnerving the Japanese and their neighbours, who want reassurances that the situation will soon be brought under control, says the BBC's Chris Hogg in Tokyo.
Meanwhile further strong aftershocks continue to rock the country. An earthquake, not considered an aftershock, of magnitude 6.2 centred south-west of Tokyo shook buildings in the capital late on Tuesday.
More than 500,000 people have been made homeless by the quake.
The government has deployed 100,000 troops to lead the aid effort.
