Japan steps up cooling operation
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Japan says it is stepping up efforts to cool overheating fuel at the tsunami-hit Fukushima Daiichi nuclear plant.
Helicopters dumped tonnes of sea water to try to prevent fuel rods melting, and media reports said water cannon had now joined in the operation on the ground.
Following the crisis, China suspended approval for new nuclear plants.
The confirmed death toll from Friday's 9.0 magnitude quake, which triggered the tsunami, has risen above 5,000.
Police say more than 5,400 people are confirmed dead and about 9,500 more are still missing.
'Deep condolences'
Japan's military CH-47 Chinook helicopters began spraying tonnes of sea water on reactors 3 and 4 at Fukushima, 220km (140 miles) from Tokyo, at 0948 local time (0048 GMT), officials said.
Continue reading the main story Analysis The attempt to use helicopters and water cannon to dump seawater on to the Fukushima power station is almost certainly unprecedented in more than half a century of nuclear power. The water was not destined for the reactors themselves - they are contained within containment systems that are designed to be sealed tight and which appear to be intact, with the possible exception of a crack in a vessel attached to No 3 reactor. The targets were cooling ponds situated above the reactors, which store fuel rods. The ponds in buildings 3 and 4 - and possibly more - are certainly short of water, possibly completely dry. This means the rods get hot, increasing the chances of radioactive substances being released. It also exposes workers to radiation from the rods. The positive development is that electric power may be restored to the plant in the coming hours, meaning pumps can be restarted - if they are still operational.
The aircraft dumped four loads before leaving the site in order to minimise the crews' exposure to radiation. On Wednesday, the helicopters were forced to abort a similar operation amid concerns over high radiation levels.
The BBC's Chris Hogg in Tokyo says the helicopters can carry an enormous amount of water but given the high winds it is difficult to know whether it has been dropped accurately.
Video footage suggests the attempts were not very successful, with most of the water falling outside the target buildings.
Later military lorries on the ground joined in with water cannon, dousing reactor 3, the NHK TV network said.
Initially police crews had tried to spray the reactor but were forced to withdraw because they would have been exposed to high radiation levels. The military vehicles, unlike those of the police, are built to allow personnel to remain inside, NHK reported.
The operation was intended to help cool the reactors and also to replenish water in a storage pond with spent fuel rods.
Officials also said they were hoping that they would restore "as soon as possible" the power supply to the plant, which is needed for the cooling system and back-up generators.
"If the restoration work is completed, we will be able to activate various electric pumps and pour water into reactors and pools for spent nuclear fuel," a spokesman for Tokyo Electric Power Company, which runs the plant, told the AFP news agency.
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The US has also been asked to fly a drone over the site to help assess the situation.
The crisis has prompted China to suspend approval of new nuclear power stations and carry out checks on existing reactors.
China currently gets about 2% of its electricity from nuclear power, but is building more reactors than any other country in the world.
In Tokyo, our correspondent says that despite an air of superficial calm there are signs of unease under the surface.
Cash machines at one bank went down for a couple of hours on Thursday afternoon - prompting speculation that some people may be stocking up on reserves of cash in case the situation deteriorates.
Britain has advised its nationals currently in Tokyo and to the north of the capital to consider leaving the area, and to keep outside an 80km radius of the Fukushima plant, in line with US state department instructions.
Continue reading the main story Fukushima Daiichi: What went wrong Reactor 1: Was first to be rocked by an explosion on Saturday; fuel rods reportedly 70% damaged
Was first to be rocked by an explosion on Saturday; fuel rods reportedly 70% damaged Reactor 2: There are fears a blast on Tuesday breached a containment system; fuel rods reportedly 33% damaged
There are fears a blast on Tuesday breached a containment system; fuel rods reportedly 33% damaged Reactor 3: Explosion on Monday; smoke or steam seen rising on Wednesday; damage to roof and possibly also to a containment system
Explosion on Monday; smoke or steam seen rising on Wednesday; damage to roof and possibly also to a containment system Reactor 4: Hit by a major blaze (possible blast) on Tuesday and another fire on Wednesday
France has urged its citizens in Tokyo to leave the country or move south. A French air force jet took 250 French nationals to South Korea, and two Air France planes are due to begin evacuations.
In areas of the north-east badly hit by the tsunami, bitter winter weather has added to the misery of survivors, though more supplies are now reported to be reaching them.
Also, Japan's Kyodo news agency quoted rescuers as saying that the search for victims had expanded over a wider area as access is improved with the clearance of debris.
About 380,000 people are currently still in temporary shelters, many sleeping on the floor of school gymnasiums.
The crisis has also continued to affect the markets - the benchmark Nikkei index fell 3.6% in early Thursday trading in Tokyo, shortly after the yen briefly hit the highest level against the US dollar since World War II.
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Japanese military helicopters have begun to drop water on the  nuclear power plant in an effort to cool reactors.

The operation began at 0948 local time (0048 UTC) today, after similar efforts were ended early yesterday due to radiation.  helicopters dropped four loads of water on reactors three and four, with officials planning up to twelve more drops before crews are forced to leave the area due to radiation.

The water drops are intended to both cool the reactors and add water to pools that hold fuel rods. These pools are believed to be almost empty; if they run out of water the fuel rods can melt and release high levels of radiation. The storage pools have a capacity of about 2,000 tonnes of water, a third of that is needed to keep fuel rods submerged. Each helicopter can carry 7.5 tonnes of water at a time.

TV footage showed helicopters dropping water from about 300 feet above the reactors. Some time after the helicopters began to drop water, military trucks started using a water cannon to spray reactor three.

The crisis at the power plant has led to the evacuation of around 70,000 people who lived within 20 kilometres of the plant, while another 140,000 are under orders to stay inside. The United States has asked its citizens who are within 80 kilometres of the plant to leave.


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