The 9.0-magnitude earthquake that slammed Japan on Friday caused both the reactor's cooling system and back-up cooling system to fail, increasing the chance of a nuclear meltdown because of the overheating of the nuclear reactor's core.

Officials just south of Fukushima reported up to 100 times the normal levels of radiation Tuesday morning, Kyodo News agency reported. While those figures are worrying if there is prolonged exposure, they are far from fatal, AP noted.

Very low levels of radiation were detected in Tokyo, the highest populated prefecture in Japan, located 150 miles south of the plant. Officials have said that at minute levels the radiation is "not a problem," Reuters reported. Tokyo's total population exceeds 13 million, with more than 15,000 residents per square mile.

"Radioactive material will reach Tokyo," Hokkaido University graduate school of environmental science professor Koji Yamazaki told Reuters, "but it is not harmful to human bodies because it will be dissipated by the time it gets to Tokyo."

Radiation levels in Maebashi, a city in Chiba prefecture, located 60 miles north of Tokyo, were 10 times the normal levels, Reuters reported, citing Kyodo News.

Of the Dai-ichi nuclear-power plant's 800 workers, 750 were dismissed by the plant operator, while 50 workers remain at the plant to try to keep the situation under control. A 20-mile no-fly zone has been imposed around the reactors.

The IAEA has reported that all units at the Fukushima, Onagawa, and Tokai nuclear power plants "are in a safe and stable condition," or a cold shutdown.

The 9.0-magnitude earthquake and ensuing tsunami that hit Japan Friday and which has crippled the Dai-ichi plant has killed more than 10,000 people, according to estimates.

The official death toll in the nation has spiked to 3,373, CNN reported.

At least 6,746 people remained missing on Tuesday, the National Police Agency said, and 1,987 were injured.

Thousands of homes were destroyed in the disaster and nearly 450,000 people were staying in emergency shelters, public broadcaster NHK reported.

-- Written by Joseph Woelfel and Theresa McCabe.

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