Japan says radiation at a quake-damaged nuclear plant has dropped after earlier reaching levels dangerous to human health.
Radiation at the Fukushima Daiichi plant spiked after an explosion and a fire earlier in the day. The March 15 blast was the third at the plant since it was damaged in a powerful 9.0-magnitude earthquake and tsunami on March 11.
Prime Minister Naoto Kan urged people within 30 kilometers of the complex to remain indoors and warned of further radiation leaks.
"Radiation has spread from these reactors and the reading of the level seems very high," he said. "And there is still a very high risk of further radioactive material coming out."
Japan also announced a 30-kilometer no-fly zone around the nuclear plant.
In Tokyo, some 240 kilometers to the south, radiation levels also rose slightly earlier but dropped later in the day.
The United Nations nuclear agency chief has said there may be limited core damage at one of the units at Fukushima.
"There is also the possibility of core damage at Unit 2 of Fukushima Dai-ichi, and the damage is estimated to be less than 5 percent of the fuel," Yukiya Amano, director-general of the International Atomic Energy Agency (IAEA), told a news conference in Vienna.
He called recent developments in Japan's nuclear crisis "worrying" but said he still believed the situation was different from that of the 1986 Chernobyl disaster.Deaths Mounting
Authorities have confirmed some 3,300 people were killed in the earthquake and tsunami, but that figure is expected to rise to as high as 10,000.
The World Health Organization (WHO) said Japan was taking the right measures to protect the local population.
Japan's nuclear safety agency maintained its rating of the accident at four on a seven-point global scale, while France's Nuclear Safety Authority (ASN) upgraded it to six. Level seven was used only once, for Chornobyl in Ukraine in 1986.
Early in the day, Reactor No. 2 at the complex was hit by a blast that appeared to have damaged one of the containment vessels. The ASN said this would explain the significant increase in detected radioactive releases.
A fire that briefly broke out at Reactor No. 4 is also believed to have released radioactivity into the atmosphere.
"There is no mistake that this is a level that can have an effect on humans," Chief Cabinet Secretary Yukio Edano said.
Edano later said radiation levels at the plant's main gate had fallen, as workers were trying to prevent meltdowns by flooding the chambers of the nuclear reactors with seawater.
On March 14, a hydrogen blast at the Fukushima plant's Reactor No. 3 followed a blast at Reactor No. 1 on March 12.
All explosions have been preceded by cooling system breakdowns.
Authorities said higher-than-normal radiation levels had been detected in Tokyo, but not at harmful levels.Bracing For More
Despite pleas for calm, residents rushed to shops to stock up on supplies.
In a sign of regional fears about radiation risks, the Chinese Embassy in Tokyo said it was preparing to send buses to remove its nationals from Japan's northeast "due to the seriousness of and uncertainty" surrounding the nuclear accident.
Water and other essentials are in short supply at a supermarket in the northwestern city of Akita
Iran's embassy in Tokyo announced Iran Air is to use its routine Thursday flight from Tokyo to Tehran as a first step to evacuate Iranians. It said the country's carrier would grant special discounts for students and their families to get back to the Iranian capital.
A number of other foreign carriers canceled flights to the Japanese capital or were diverting all Tokyo-bound flights to other Japanese cities.
Russian officials said radiation levels in Russia's Far East stayed within normal levels. But the Interfax news agency quoted Russia's military as saying it was on alert to evacuate residents if required.
The UN weather agency said that winds were currently blowing radioactive material toward the ocean and that there were "no implications" for Japan or countries nearby.
The disaster prompted several countries, including Russia, to review the safety of their own nuclear installations.
German Chancellor Angela Merkel said Berlin would provisionally shut down seven nuclear reactors for three months pending a safety assessment.
"In light of the situation [in Japan], we will carry out a safety check of all nuclear plants," she said. "The federal government and the states [governments] agreed on that. Those nuclear power plants which began operation before 1980 will be provisionally shut down for the duration of the [three-month] moratorium. They will be out of order."
The unfolding nuclear crisis comes as Japan is still reeling from the double disaster of the March 11 earthquake and tsunami.
Millions of people are without water, heating, or enough food with temperatures at night near freezing. Hundreds of thousands are homeless.
And the government is only beginning to count the likely economic cost of what Prime Minister Kan has called the country's worst crisis since World War II.
According to Singapore's DBS Bank, the twin disasters would cost Japan's economy about $100 billion, or about 2 percentage points of its annual gross domestic product.
compiled from agency reports