Operators of a quake-crippled nuclear plant in Japan said they would try again on Thursday to use military helicopters to douse overheating reactors and avert disaster after an earlier attempt was abandoned because of high radiation at the site.
While officials scrambled to contain the nuclear crisis with a variety of patchwork fixes, health experts said panic over radiation leaks from the Daiichi plant may divert attention from potentially worse threats to survivors of Friday's 9.0 magnitude quake and tsunami, such as the cold or access to fresh water.
The head of the world's nuclear watchdog, meanwhile, said while it was not accurate to say things were "out of control" in Japan, the situation was "very serious", with core damage to three units at the plant.
Japan's government said radiation levels outside the plant's gates were stable but, in a sign of being overwhelmed, appealed to private companies to help deliver supplies to tens of thousands of people evacuated from around the complex.
Bulldozers attempted to clear a route to the reactor, about 240 kms (150 miles) from Tokyo, so firetrucks could gain access and try to cool the facility using hoses.
"People would not be in immediate danger if they went outside with these levels. I want people to understand this," Chief Cabinet Secretary Yukio Edano told a news conference, referring to people living outside a 30-km (18-mile) exclusion zone.
High radiation levels on Wednesday prevented a helicopter from dropping water into the No 3 reactor to try to cool its fuel rods after an earlier explosion damaged the unit's roof and cooling system.
Officials from the Tokyo Electric Power Co said shortly after midnight (1500 GMT) that they would ask the military to make a second attempt later on Thursday.
The plant operator described No 3 -- the only reactor at that uses plutonium in its fuel mix -- as the "priority". Plutonium, once absorbed in the bloodstream, can linger for years in bone marrow or liver and lead to cancer.
The situation at No 4 reactor, where the fire broke out, was "not so good", the plant operator added, while water was being poured into reactors No 5 and 6, indicating the entire six-reactor facility was now at risk of overheating.
"Getting water into the pools of the No. 3 and No.4 reactors is a high priority," Said Hidehiko Nishiyama, a senior official at Japan's Nuclear and Industrial Safety Administration, adding the pool for spent fuel rods at No. 3 was heating up while No. 4 remained a concern.
"It could become a serious problem in a few days," he said.
Nuclear experts said the solutions being proposed to quell radiation leaks at the complex were last-ditch efforts to stem what could well be remembered as one of the world's worst industrial disasters.
"This is a slow-moving nightmare," said Dr Thomas Neff, a physicist and uranium-industry analyst at the Massachusetts Institute of Technology.
Japanese Emperor Akihito, delivering a rare video message to his people on Wednesday, said he was deeply worried by the crisis which was "unprecedented in scale".
"I hope from the bottom of my heart that the people will, hand in hand, treat each other with compassion and overcome these difficult times," the emperor said.
Panic over the economic impact of last Friday's massive earthquake and tsunami knocked $620 billion off Japan's stock market over the first two days of this week, but the Nikkei index rebounded on Wednesday to end up 5.68 percent.
Nevertheless, estimates of losses to Japanese output from damage to buildings, production and consumer activity ranged from between 10 and 16 trillion yen ($125-$200 billion), up to one-and-a-half times the economic losses from the devastating 1995 Kobe earthquake.
The catastrophe risk modeling firm Eqecat said Friday's earthquake caused insured losses of between $12 billion and $25 billion, making it one of the costliest natural disasters in history for global insurers.
Damage to Japan's manufacturing base and infrastructure is also threatening significant disruption to the global supply chain, particularly in the technology and auto sectors.
Embassies Urge Citizens To Leave
Scores of flights to Japan have been halted or rerouted and air travellers are avoiding Tokyo for fear of radiation. On Thursday the US Embassy in Tokyo urged citizens living within 50 miles (80 kms) of the Daiichi plant to evacuate or remain indoors " as a precaution".
The warning was not as strong as those issued earlier by France and Australia, which urged nationals in Japan to leave the country. Russia said it planned to evacuate families of diplomat on Friday.
In a demonstration of the qualms about nuclear power that the crisis has triggered around the globe, China announced that it was suspending approvals for planned plants and would launch a comprehensive safety check of facilities.
China has about two dozen reactors under construction and plans to increase nuclear electricity generation about seven-fold over the next 10 years.
Russian President Dmitry Medvedev said nuclear power was safe provided power stations were built in the right place and designed and managed properly. Russia ordered checks at nuclear facilities on Tuesday.
In Japan, the plight of hundreds of thousands left homeless by the earthquake and devastating tsunami that followed worsened following a cold snap that brought snow to worst-affected areas.
Supplies of water and heating oil are low at evacuation centres, where many survivors wait bundled in blankets.
"It's cold today so many people have fallen ill, getting diarrhea and other symptoms," said Takanori Watanabe, a Red Cross doctor in Otsuchi, a low-lying town where more than half the 17,000 residents are still missing.
The National Police Agency said it has confirmed 4,314 deaths in 12 prefectures as of midnight Wednesday, while 8,606 people remained unaccounted for in six prefectures.
Japanese officials said they were talking to the U.S. military about possible help at the plant.
Concern has mounted that the skeleton crews dealing with the crisis might not be big enough or were exhausted after working for days since the earthquake damaged the facility.
Authorities withdrew 750 workers for a time on Tuesday, briefly leaving only 50. All those remaining were pulled out for almost an hour on Wednesday because radiation levels were too high, but they were later allowed to return. By the end of the day, about 180 were working at the plant.
In the first hint of international frustration at the pace of updates from Japan, Yukiya Amano, director general of the International Atomic Energy Agency, said he would fly to Japan as soon as possible to glean first hand information on the crisis.
Several experts said the Japanese authorities were underplaying the severity of the incident, particularly on a scale called INES used to rank nuclear incidents. The Japanese have so far rated the accident a four on a one-to-seven scale, but that rating was issued on Saturday and since then the situation has worsened dramatically.
France's nuclear safety authority ASN said on Tuesday it should be classed as a level-six incident.
At its worst, radiation in Tokyo reached 0.809 microsieverts per hour on Tuesday -- 10 times below what a person would receive if exposed to a dental x-ray. For Wednesday, radiation levels were barely above average.
But many Tokyo residents stayed indoors.