There is no evidence of a significant spread of radiation from Japan's crippled nuclear plants, the World Health Organization said on Wednesday, calling on people to stay calm and not spread rumors.
Japan's nuclear crisis appeared to be veering out of control after workers withdrew briefly from a stricken power plant because of surging radiation levels, but desperate efforts to avert a catastrophic meltdown quickly resumed.
Early on Wednesday, another fire broke out at the earthquake-crippled facility, which has sent low levels of radiation wafting into Tokyo in the past 24 hours, triggering fear in the capital and international alarm.
Radiation levels in Russia's Far East rose slightly on Tuesday but stayed within normal levels, Russian officials said.
Unfounded messages have circulated online and via text messages across parts of Asia that a radiation cloud from Japan was spreading rapidly. Weather forecasters, however, expect winds to blow the radiation out across the Pacific.
"The World Health Organization 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," Michael O'Leary, WHO's representative in China, said in a statement.
The WHO is working with Japan's government and the International Atomic Energy Agency to assess the situation, and does not think there is significant risk to health for people outside a 30-km (20-mile) exclusion zone around the facility, he added.
"Rumors have been circulating by text messaging and other means of a threatening radiation cloud spreading across Asia and beyond from the damaged nuclear facilities in Japan," O'Leary said.
"Governments and members of the public are encouraged to take steps to halt these rumors, which are harmful to public morale. The situation is being monitored closely. More information would be shared promptly should the risk become more widespread."
One text message, which purported to be based on a news report, warned of the imminent arrival of radiation over the Philippines, advising people to stay out of the rain and swab their necks with iodine.
The messages caused alarm in the Philippines and even led some schools to close.
"Let us not compound the issue by spreading hoaxes or wrong messages because this is very detrimental to the normal activities of the people," said Philippine Volcanology and Seismology Director Renato Solidum.
Guan Anping, a lawyer in Beijing, said he was staying indoors for the next few days, and even taking meals in his office. He had also advised friends to do the same, and rejected suggestions that such caution was unnecessary.
"Countries near to Japan are sure to be affected," he said of the radiation risk. "Most people won't be as cautious as me, but for the next few days I say it makes sense to play it safe."
Many users of China's Twitter-like Weibo micro-blogging site appeared similarly unconvinced that they were safe.
"Who can tell me, is there really nuclear radiation!!! Is there any!!! Do I need to buy white clothes, iodine tablets, a mask, what should I need to buy?" wrote one user.
Many Weibo users said the rumors had led to a run on iodine and masks at pharmacies in Beijing and Shanghai.