Radiation levels soared and staff fled the stricken Fukushima nuclear power plant in Japan yesterday when another fire broke out.
The French government called the situation in north-eastern Japan "a catastrophe" and advised citizens to leave the country. Plans were made to send water cannon to the nuclear complex to cool an overheating reactor.
In a rare televised address Emperor Akihito said the country had suffered a tragedy "unprecedented in scale" and admitted he was "deeply worried" about events at Fukushima.
The worst crisis in the nuclear industry since the Chernobyl disaster in 1986 developed because cooling systems at the plant were knocked out by the 9.0-magnitude earthquake and subsequent tsunami that struck last Friday.
A fire at the building housing the No 4 reactor broke out yesterday morning. Within several hours the plant's operator, Tokyo Electric Power Co (Tepco), reported flames could no longer be seen.
Later, however, smoke or steam billowed from the No 3 reactor, forcing staff trying to stabilise the plant to withdraw as radiation levels increased. Plans to pour water on to the reactor by helicopter had to be shelved because of worries over radioactivity.
The National Police Agency has been asked to send a water cannon to douse the No 4 reactor facility, which contains a storage pool of spent fuel, a move seen as a desperate measure to avert a large-scale radiation leak.
The No 4 reactor, inactive when the tsunami struck, may present the greatest threat because it lacks the containment structures surrounding the nuclear material in the neighbouring reactors.
China announced yesterday it was stopping approval of new nuclear power plants and inspecting those under construction. The French president, Nicolas Sarkozy, called for a special G20 energy summit.
Radioactive material was detected yesterday in tapwater in Fukushima prefecture, although state authorities insisted the level did not pose health risks. In Ibaraki prefecture to the south, radiation levels reached 300 times normal.
France sent planes from its national carrier to help citizens to leave the country and advised those who remained to travel south of Tokyo.
The French industry minister, Eric Besson, said the Japanese authorities had "lost control" of the Fukushima plant and, in a further indication of the seriousness of the situation, the EU energy commissioner, Guenther Oettinger, warned of "further catastrophic events" and described the nuclear plant as "effectively out of control".
Many Tokyo residents were reported to be heading south to get further away from the stricken nuclear plant, about 240km from the city. Reports showed empty streets in the capital.
The International Federation of Red Cross and Red Crescent Societies insisted the capital was safe.
In his televised address, the 77-year-old emperor said he was "deeply hurt by the grievous situation in the affected areas".
"The number of deceased and missing increases by the day and we cannot know how many victims there will be. My hope is that as many people as possible are found safe," he said.
Despite heavy snowfalls in the crisis-hit areas, including Sendai, the city of one million that was devastated in Friday's tsunami, many rescue teams continued to work, pulling bodies from mud and piles of rubble.
Yin Guanghui, a Chinese rescuer working in the town of Ofunato, said: "The strong smell of bodies and the dirty seawater make searching extremely difficult,
"Powerful waves in the tsunami would repeatedly hit houses in the area. Anyone trapped under the debris would be drowned in no time, without any chance to survive."
The official death toll has risen to 4,164, and 7,843 more are missing, although the eventual number of victims will probably be higher still. Many bodies will never be found. Another 7,558 people are reported injured in the disaster.
More than 2,400 shelters are housing about 430,000 people forced to flee their homes when waves of up to 10 metres slammed into the coast and travelled several kilometres inland.
As forecasters warned temperatures could dip to below zero, the national broadcaster NHK gave residents survival tips, showing how they could boil water with just empty cans and candles, and keep warm by wrapping their bodies in newspaper and cling-film.
Plans were announced to build nearly 33,000 temporary housing units in three of the hardest-hit prefectures: Iwate, Fukushima and Miyagi.
Looking further ahead, analysts predicted reconstruction could take five years. The government said it was considering setting up a dedicated ministry to oversee rebuilding efforts.
The governor of Fukushima said residents there, suffering first the tsunami and now being front-line in the nuclear crisis, have been "pushed to the limit".
Yet in the face of adversity survivors who in many cases had lost everything showed a stoical determination. In an NHK report, many had gathered at a restaurant in Miyagi to prepare food together.
"If people help each other, there will be a better future ahead," an elderly man told the station.