The World Health Organisation says the radiation risk from Japan's nuclear crisis remains highly localised, with no sign of an immediate threat elsewhere in Asia, as Japan raises the nuclear alert level to 5.
Michael O'Leary, head of WHO in China, said Friday there was "no evidence of a signicant spread of radioactive material" beyond the immediate area around the Fukushima nuclear plant.
Workers are fighting to cool the overheating reactors at the plant critically damaged by last week's earthquake and tsunami.
The zone within 20km of the reactors has been evacuated, while people within 30km were told to stay indoors.
Health experts say there is little risk beyond that, including in the capital of Tokyo, 220km away.
Still, China and other neighbouring countries increased monitoring of radiation levels.
Japan raises nuclear alert level
Japan's nuclear safety agency raised the Fukushima accident level to five from four on the international scale of gravity for atomic accidents, which goes as high as seven.
The agency's decision puts the Fukushima crisis on the same level as the 1979 accident at Three Mile Island in Pennsylvania.
France's Nuclear Safety Authority rates the Fukushima crisis at six on the scale. The Chernobyl disaster is put at seven, the highest.
Level 5 indicates "an accident with wider consequences", according to the International Nuclear Event Scale (INES), while level four means there has been an "accident with local consequences."
The March 28, 1979 accident at Three Mile Island was a partial reactor meltdown that led to "very small" releases of radioactivity, according to the US Nuclear Regulatory Commission (NRC). It caused no casualties.
The April 26, 1986 explosion at the Soviet atomic power plant in Chernobyl was the world's worst nuclear disaster.
Unleashed by an unauthorised technical experiment, it spewed radioactive dust over swathes of Ukraine, Belarus, Russia and western Europe.
The death toll ranges from a UN 2005 estimate of 4,000 to tens or even hundreds of thousands, proposed by non-governmental groups.
