"I don't know what exactly happened out there," she said. "I only want to have something to protect myself."

Reacting to mounting public concern, experts and authorities warned of the possibility of overreactions to Japan's nuclear emergency.

The Chinese Center for Disease Control and Prevention released a statement on Wednesday, saying that taking stable iodine pills can help prevent the human body from absorbing radioactive iodine, and that the pills should be taken under the instruction of the government after its appraisal of the situation.

"There is no need to panic now," said Wang Zhongwen, a researcher of the radiation safety department under the China Institute of Atomic Energy.

"It's still very low levels of radiation, not enough to have an effect on human health."

Dr Michael O'Leary, the World Health Organization's representative in China, released a statement on Wednesday saying that there is no evidence showing that radiation leaked from the Japanese nuclear plant has spread to other countries or that the health dangers have increased for those living outside the 30 kilometers exclusion zone established by the Japanese.

China's Ministry of Environmental Protection said China had not been affected by the radiation leaks in Japan by Wednesday afternoon.

Since March 12, the ministry's department of nuclear safety management has used its website to post radiation figures twice a day for 42 Chinese cities, as well as for areas surrounding the country's nuclear power plants. The readings are all within safe levels.

A report from the monitoring agency under the Shanghai environmental protection bureau showed that no radioactive materials have been detected so far in Shanghai.

To monitor radiation levels, Northeast China's Heilongjiang province has set up four mobile emergency stations along its eastern regions bordering Russia.

The stations had not detected abnormal levels of radioactive substances by Wednesday noon, said Xu Lijuan, a deputy director of Heilongjiang's radiation monitoring station.