By Hiroyuki Kachi

TOKYO (Dow Jones)--Radiation levels in the Tokyo area were around typical background levels on Friday afternoon, while in areas close to the quake-damaged Fukushima nuclear power plant they remained high but still below levels that would pose a threat to human health, officials said.

In a separate move, the International Atomic Energy Agency will begin measuring radiation levels, staring with Tokyo, as early as Friday night, said Yukiya Amano, director general of IAEA.

The Tokyo Metropolitan Government said Friday on its website that radiation levels in downtown Tokyo stood at 0.047 microsievert an hour around 1000 GMT. That compares with the 0.035 microsievert an hour a person would typically be exposed to in Shinjuku district of downtown Tokyo due to background radiation.

"If we can measure levels at several locations in Tokyo, many people will feel assured," Amano said.

A team consisting of a nuclear safety expert, two experts in measuring radiation levels, and one Japanese coordinator is planning to go to the Fukushima nuclear power site, but some logistic support may be required since they are carrying heavy equipment, Amano said.

Levels remained higher in Fukushima Prefecture, closer to the Fukushima Daiichi nuclear plant, which has become a matter of international concern after a massive earthquake on March 11 knocked out the cooling systems of several of the reactors there. Authorities Friday continued to pour water onto the troubled Fukushima Daiichi nuclear-power complex using fire trucks.

Japanese authorities were evacuating people within a 20-kilometer radius and telling those within an 30-kilometer radius of the complex to stay inside.

At one point about 30 kilometer north west of the Fukushima plant, just outside the evacuation zone, high radiation levels of 150 microsieverts were measured around 0432 GMT Friday, according to the Ministry of Education, Culture, Sports, Science and Technology.

A ministry official said the point again detected high radiation possibly because radioactive air was captured in a dip there, noting that radiation levels fluctuate depending on landscape and direction of the wind. But he said the ministry still can not exactly tell.

If a human stays there for seven hours, the resultant radiation dose would exceed the 1,000 microseivets that an ordinary human absorbs in public spaces over a one year period.

"I would say do not stay there for over a long period of time," the official said, adding that such levels would not cause immediate health problems.

In another point about 35 kilometers west of the plant, radiation worth 0.5 microsievert was detected. Several van traveling these area with radiation measuring equipment compiled the data.

A chest X-ray typically exposes the patient to a radiation dose of around 100 microsieverts, according to the Radiological Society of North America. The U.S. Nuclear Regulatory Commission sets the annual occupational dosage limit for workers who deal with radiation at 50,000 microsieverts and the limit per nuclear event at 10,000 microsieverts. The U.S. Environmental Protection Agency advises that a dose of 500,000 microsieverts can cause nausea, while 4 million microsieverts can be fatal without major medical care.

Separately, Fukushima Prefecture said on its website that it measured radiation of 10.80 microsieverts around 1100 GMT Friday in Fukushima City, about 60 kilometers northwest of the plant. It said it detected 2.46 microsieverts an hour in Koriyama City, around 60 kilometers west of the plant, and 1.00 in Iwaki City, about 40 kilometers southwest of the plant, around 1100 GMT. Normal levels at these locations range between 0.04 and 0.06 microsieverts.

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