Typical amounts of radiation in Hong Kong exceed those in Tokyo even as workers struggle to contain a crippled nuclear plant in northern Japan, indicating concerns about spreading contamination may be overblown.

The radiation level in central Tokyo reached a high of 0.109 microsieverts per hour in Shinjuku Ward yesterday, data from the Tokyo Metropolitan Institute of Public Health show. That compares with 0.14 microsieverts in the Kowloon district of Hong Kong, the Hong Kong Observatory said on its website. A person is exposed to 50 microsieverts from a typical x-ray.

Many countries have naturally occurring radiation levels that exceed Tokyo's, said Bob Bury, former clinical lead for the U.K.'s Royal College of Radiologists. A 30-fold surge in such contamination in Tokyo prompted thousands of expatriates to leave Japan after the March 11 tsunami knocked out power at Tokyo Electric Power Co.'s Fukushima Dai-Ichi nuclear plant, triggering the crisis. Radiation in Tokyo is barely above levels in London and New York even now, analysts said.

"The situation in Japan looks set to follow the pattern of Chernobyl, where fear of radiation did far more damage than the radiation itself," Bury said in an e-mail referring to the 1986 accident in the former Soviet Union, the world's worst nuclear disaster. "Whatever the radiation in Tokyo at the moment, you can be fairly sure it is lower than natural background levels in many parts of the world."

And a section on natural radiation:

Natural Radiation

Natural radiation makes up about 85 percent of the global total, according to the World Nuclear Association. Manmade contributors include medicine and buildings, as well as the nuclear industry, which accounts for 1 percent of the total, the association says. Foodstuffs also contain radiation, and a 135- gram (4.8-ounce) bag of Brazil nuts has a dose of about 10 microsieverts, according to the U.K. agency.

Other activities that enhance naturally occurring radiation levels include mining, milling and processing of uranium ores and mineral sands, manufacturing and use of fertilizers and the burning of fossil fuels, according to a 2008 report by the International Atomic Energy Agency.

The highest level of background radiation is in the state of Kerala and city of Chennai in southern India, where people receive average doses above 30 millisieverts per year, or 3.42 microsieverts an hour, according to the World Nuclear Association.

India has vast amounts of thorium in its soil. A millisievert is 1,000 microsieverts.

In Brazil and Sudan, exposure can reach 40 millisieverts a year or 4.57 microsieverts an hour, the Association says