"To date, we don't have any information of a significant spread of radioactive material beyond the evacuation zone," said Michael O'Leary, head of WHO in China. "At present, we still understand it's very confined. That's why there's an evacuation zone around the nuclear reactor itself."
Workers are fighting to cool the overheating reactors at the Fukushima nuclear plant in northeast Japan critically damaged by last week's earthquake and tsunami. The zone within 12 miles (20 kilometers) of the plant has been evacuated, while people within 20 miles (30 kilometers) were told to stay indoors.
Health experts say there is little risk beyond that, including in the capital of Tokyo, 140 miles (220 kilometers) away.
Still, China and other neighboring countries increased monitoring of radiation levels, and fears of radioactive contamination have prompted panic-buying across China of iodized salt.
Shoppers in Beijing, Shanghai and other parts of China have stripped supermarket shelves empty of table salt in recent days in the false belief that it either wards off radiation injuries or that the nation's supply would be contaminated by radioactive fallout.
Experts have said the first rumor is not true and the second is unlikely: any catastrophe at the Japanese nuclear plant would most likely affect the immediate area, and wind patterns usually blow away from China at this time of year.
The rumors are part of a swirl of misinformation regarding Japan's nuclear emergency.
China Central Television reported Friday that China's salt makers have 2 million tons of salt in reserves and have stepped up production as the government seeks to control rampant sales.
"The panic buying at such a large scale tests our coordination and distribution abilities, but we have confidence we can resume the normal supply to the market within 2 weeks," Dong Yongsheng, deputy general manager of China National Salt Industry Company, told CCTV.
Beijing started a seven-day inspection on table salt prices. Those found to have illegally hiked prices will be punished, the city government said.
The National Marine Environmental Forecasting Center reported late Thursday that air and seawater levels in China are not under immediate threat. Ocean and wind currents are moving east, so any contaminants would be pushed into the Pacific Ocean, the forecasting center said in a statement. China lies to the west of Japan.
China said it was providing 30 million yuan ($4.6 million) worth of humanitarian assistance — along with delivering 10 tons of bottled water Thursday at the request of the Japanese government, the official Xinhua News Agency reported. Earlier this week, the first batch of Chinese relief supplies — blankets, tents and emergency lights — arrived.