SHANGHAI - A netizen surnamed Chen in Hangzhou, East China's Zhejiang province, was held in custody for 10 days and fined 500 yuan ($76) by local police on Sunday for spreading salt rumors online last Tuesday.

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Working at a computer company, the 31-year-old man posted a hoax on a local online forum, saying that the radiation leaked from the Fukushima Daiichi nuclear power plant in Japan had polluted the sea off the coast of eastern Shandong province. He encouraged people to store salt and dried kelp. He also said they should try to avoid eating seafood for a year.

The post spread rapidly on the Internet and caused local residents to panic, according to the police.

Chen said he received the false information when chatting with a friend online.

In Shanghai, the local police said on Friday last week that two men will be faced with prosecution for disseminating rumors that said the city will be severely contaminated by the nuclear leak in Japan, Shanghai-based news portal Xinmin.cn reported.

Among the other causes of the panicked purchases of salt were rumors contending that eating iodized salt could prevent people from being harmed by radiation leaked from a Japanese nuclear plant.

Supermarket shelves in places like Zhejiang, Guangdong, Jiangxi and Sichuan provinces and in large cities like Beijing and Shanghai were nearly devoid of salt by Thursday.

However, by Saturday last week, some consumers who had realized that the hoarding of salt would not be useful in countering a leak of nuclear radiation had started to return to supermarkets to try to get their money back.

A university professor believes insufficient releases of reliable and timely information by the government also contributed to panicked purchases of salt in China.

"The panic perhaps could have been avoided if the government had released enough reliable information in response to the recent series of disasters in Japan," said Qiu Liping, a professor in the sociology department at Shanghai University.

He added that food safety is perhaps the largest concern in China at present.

A related rumor spread on the Internet on Sunday said that a man from Cixi, in Zhejiang province, died from eating too much iodized salt. Cixi authorities proved that story to be false.

"The public feels anxious because it doesn't receive enough scientific knowledge from day to day," said Qiu.

Qiu said the elderly and the middle-aged were among those most likely to buy salt in response to the rumors. Many of them had picked up the false information from gossip.

"I got my earthquake fears from another old lady in the market, who made me believe that Shanghai will be severely affected soon," said Lu Huizhen, an 82-year-old local resident who was stopped by her daughter from taking all her savings out from a bank and moving inland.

"The government should find a good way to release accurate and accessible information after emergencies," Qiu said. "This will ensure citizens believe the authorized information instead of rumors."