Explosions and fires at the Fukushima Daiichi plant have damaged its cooling systems
A rise in radiation levels at Japan's stricken Fukushima nuclear plant has forced workers to suspend operations, a government spokesman says.
He was speaking after smoke was seen billowing from reactor three. Earlier, a blaze struck reactor four for the second time in two days, reports the BBC.
Friday's 9.0-magnitude earthquake and tsunami, which killed thousands, damaged the plant's cooling functions.
The site has been hit by several explosions, triggering radiation leaks.
Francehas urged its nationals living in Tokyo to leave the country or head to southern Japan because of the risk of radiation.
On Wednesday, Japanese Cabinet Secretary, Yukio Edano told a news briefing that workers at the Fukushima Daiichi plant had been withdrawn following the sudden rise in radiation levels.
It is believed that about 50 employees had been working at the plant - 220km (140 miles) north of Tokyo - to try to cool its four reactors and avert a meltdown.
Edano also said that the radiation levels were now falling from 1,000 millisieverts on Wednesday morning to 600-800.
But that was still more than average, Edano said, adding that "workers cannot carry out even minimal work at the plant now. Because of the radiation risk, we are on standby."
The new fire at reactor four was reported early on Wednesday. Three hours later, Japan's nuclear safety agency said flames could no longer be seen.
But white smoke was later seen rising from reactor three. Officials are investigating the cause of both incidents and the damage done, with Edano saying the smoke was probably steam from the evaporation of water, which caused the higher radiation.
"A part of the containment vessel is broken and it seems like the vapour is coming out from there. So... [it] appears to be that vapour is coming out from the broken part."
On the surface, Tokyo is still deceptively normal.
But look a bit closer and the concern people are feeling here about radiation leaks is clear.
There are fewer cars on the streets than normal. There are queues, an hour long and more, for petrol. Shelves are bare in some shops as people buy up food.
Tokyo's stock market has seen two days of heavy losses.
Foreigners have been leaving in increasing numbers. Adding to the jitters just as people were going to bed on Tuesday night there was another tremor, this time a bit larger, and longer than before.
But most people remained inside their homes and went to sleep.
On Tuesday morning, another fire broke out in the spent fuel storage pond at reactor four.
The reactor had been shut down before the quake for maintenance, but its spent fuel rods are still stored on the site.
Kyodo news agency says the storage pool may be boiling and further radiation leaks are feared.
The Tokyo Electric Power Co (TEPCO), which operates the Fukushima plant, said it may pour water and fire retardant from helicopters to stop fuel rods from being exposed to the air and releasing even more radioactivity.
The crisis at the plant - which has six nuclear reactors - began when the earthquake struck. Explosions rocked the buildings housing reactors one and three on Saturday and Monday.