Radioactivity levels have fallen sharply at a Japanese nuclear power plant damaged by last week's earthquake and tsunami.
The United Nation's nuclear watchdog says the latest data indicates radioactivity levels have fallen sharply at at the Fukushima Daiichi nuclear power plant.
On Monday, the number 2 reactor at the plant became the third to explode in four days.
A fire also briefly broke out at the number 4 reactor, and is believed to have caused radioactive leaks.
The reactor had been shut down for maintenance.
Officials have extended the danger zone around the nuclear plant.
They are warning residents still left within 20 kilometres to evacuate.
Those 20 to 30 kilometres from the plant are being urged to stay indoors and shut their windows.
CNN is reporting that Japan has imposed a no-fly zone over the nuclear plant due to detected radiation.
Before the latest explosion - the fourth in four days - Prime Minister Naoto Kan said radiation levels had risen considerably, with a risk of radiation leaking into the atmosphere, and a meltdown was likely.
Chief Cabinet Secretary Yukio Edano says radiation levels at the nuclear plant have reached as high as 400 milisieverts an hour, thousands of times higher than readings taken before the latest blasts.
He emphasised that those levels were recorded at the Daiichi plant and that the "further away you get from the power plant or reactor, the value should go down".
However, authorities are telling everyone within a 20-kilometre radius of the plant to leave, with a new warning for people within 10 kilometres of the nearby Fukushima Daini plant to do the same.
The French embassy in the capital warned in an advisory that a low level of radioactive wind could reach Tokyo within 10 hours.
In a statement posted on its Japanese website, the embassy urged French citizens in the city to stay indoors, close the windows and not to panic.
Two explosions occurred within hours on Tuesday, with the reactor 4 blast preceded by a blast in reactor 2. The blast in reactor 4 also caused a fire, which local media are reporting has now been put out.
Earlier, explosions also occurred in reactors 1 and 3.
Authorities had been trying to prevent meltdowns by flooding the reactor chambers with sea water to cool them down after water levels dropped, exposing the fuel rods.
More of the workers remaining at the Fukushima Daiichi plant were evacuated after the third explosion.
The two plants are about 250km north-east of Tokyo.
Japan calls on IAEA
Meanwhile, Japan has asked the International Atomic Energy Agency (IAEA) to send a team of experts and has requested from the United States additional equipment to help provide water and other resources to keep the reactors cool.
Before the latest explosion and fire, France's nuclear authority said the Fukushima failure could be on par with the 1979 Three Mile Island meltdown in the United States.
The emergency has prompted Germany and Switzerland to halt nuclear programs as European governments scramble to review safety.
About 150 reactors are scattered across the continent in half as many nuclear power plants - some located in seismic areas.
The European Union has convened emergency talks of energy ministers, national nuclear safety officials and big nuclear companies. Italy and Poland have decided to rethink prior decisions to invest in nuclear energy.