China on Thursday urged Japan to provide prompt, precise information about its nuclear crisis in a bid to control a flurry of rumors sweeping the region about possible dangers.

Worried shoppers stripped stores of iodized salt in Beijing, Shanghai and other parts of China on Thursday in the false belief that it either wards off radiation injuries or that the nation's supply would be contaminated by fallout from a crippled Japanese nuclear power plant.

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 the year. The rumors are part of a swirl of misinformation crisscrossing the region in the wake of Japan's nuclear emergency.

In China, text messages on mobile phones circulated about nuclear plumes spreading from Japan throughout Asia. Rumors also spread that iodized salt was adequate protection against radiation sickness.

Chinese media reported that some people were also worried that radiation would seep into sea water and potentially contaminate China's future salt supply.

Supermarkets in the capital of Beijing and many cities across the country have run out of salt in the last several days as the wave of panic buying spread across provinces from eastern Zhejiang to southern Guangdong to western Sichuan.

The Foreign Ministry called on Japan to provide information swiftly.

"We hope the Japanese side will release information to the public in a timely and precise manner as well as its evaluation and prediction of the situation," ministry spokeswoman Jiang Yu told a regular briefing, when asked about the panic buying. She added, "I do not see any necessity to panic."

Potassium iodide can be used to help protect the thyroid gland from radiation injury, but regular table salt doesn't contain enough iodine, according to health experts.

Still, prices of salt jumped five or 10-fold in southern Guangdong, the Internet portal sina.com reported.

In Shanghai, Dong Linhua, a 57-year-old factory worker, said he wanted to buy just 2.2 pounds (1 kilogram) of salt but could not even find that.

"Salt is not available in any of the shops," he said. Dong said he didn't believe the rumors but wanted to have salt for his family.

The Chinese government is trying to counter the fears. The country's largest salt maker, China National Salt Industry Corp., issued a statement Thursday saying ample reserves were available and that "panic-buying and hoarding is unnecessary," according to the official Xinhua News Agency.

A range of national and provincial government agencies issued notices to crack down on hoarding and spreading rumors and warned of fines of up to 2 million yuan ($300,000) for price gouging.

The Ministry of Health posted information on its website telling people that taking regular table salt cannot prevent the dangerous effects of radiation. An adult would need to ingest 6.6 pounds (3 kilograms) of salt at one time, the ministry said.

Michael O'Leary, head of the World Health Organization in China, called on governments and individuals to "take steps to halt these rumors, which are harmful to public morale."

O'Leary said WHO "would like to assure governments and members of the public that there is no evidence at this time of any significant international spread from the nuclear site."

Rumors also affected other countries. In Vietnam, schools kept students indoors while some companies allowed employees to leave early to avoid a rainfall after rumors spread that it would burn skin and cause cancer.

A similar scare in the Philippine capital led a university to cancel classes Monday.

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Associated Press researchers Yu Bing and Fu Ting contributed to this report.