Workers were ordered to withdraw briefly from a stricken Japanese nuclear power plant on Wednesday after radiation levels surged, a development that suggested the crisis was spiralling out of control.

Just hours earlier another fire broke out at the earthquake-crippled facility, which has sent low levels of radiation wafting into Tokyo in the past 24 hours, triggering fear in the capital and international alarm.

Workers were trying to build a road so fire trucks could reach reactor No. 4. Flames were no longer visible at the building housing the reactor, but TV pictures showed rising smoke or steam. A helicopter was also preparing to pour water on to No. 3 reactor -- whose roof was damaged by an earlier explosion -- to try to cool its fuel rods, broadcaster NHK said.

Nuclear experts said the solutions being proposed to quell radiation leaks at the Daiichi complex in Fukushima, 240 km (150 miles north of Tokyo, 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 research affiliate at the Center for International Studies, which is part of the Massachusetts Institute of Technology.

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.

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.

Scores of flights to Japan have been halted or rerouted, air travellers are avoiding Tokyo for fear of radiation, and on Wednesday France urged its nationals in the city either to leave Japan or head to the south of the country.

The plight of hundreds of thousands left homeless by the quake and devastating tsunami that followed worsened overnight following a cold snap that brought snow to some of the worst-affected areas.

While the death toll stands at around 4,000, more than 7,000 are listed as missing and the figure is expected to rise. At the Fukushima plant, authorities have spent days
desperately trying to prevent water which is designed to cool the radioactive cores of the reactors from evaporating, which would lead to overheating and possibly a dangerous meltdown.

Concern now centres on damage to a part of the No.4 reactor building where spent rods were being stored in pools of water, and also to part of the No.2 reactor that helps to cool and trap the majority of cesium, iodine and strontium in its water.

Japanese officials said they were talking to the U.S. military about possible help at the plant. Concern mounted earlier 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 on Tuesday, 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.

Arnie Gundersen, a 39-year veteran of the nuclear industry, now chief engineer at Fairwinds Associates Inc and who worked on reactor designs similar to Daiichi plant, said 50 or so people could not babysit six nuclear plants. "That evacuation (of 750 workers) is a sign they may be throwing in the towel," Gundersen said.