Raising alarms, Japanese authorities said radiation leaked from the quake hit Fukushima Dai-ichi nuclear plant could be high enough to endanger humans.
In a nationally televised statement, Prime Minister Naoto Kan said the level seems very high and there is still a very high risk of more radiation coming out.
He asked an estimated 140,000 people living within 30 kms of the facility north of capital to remain indoors and to conserve power as threat loomed large of Japan's crisis turning into a Chernobyl-like disaster.
Chief Cabinet Secretary Yukio Edano said a fourth reactor at the complex had been extinguished after catching fire -- but had released radiation during the process.
Meanwhile, The French embassy in the capital warned in an advisory that a low level of radioactive wind could reach Tokyo, 240km south of Fukushima.
Accordin to Kyodo News minute levels of radiation have already been detected in Tokyo and radiation levels in Saitama, near Tokyo, are 40 times normal levels.
This is the worst nuclear crisis Japan has faced since the atomic bombing of Hiroshima and Nagasaki during World War II.
On Monday, the U.S. Geological Survey updated the magnitude of the quake from 8.9 to 9.0, making it the fourth-largest in the world since 1900.
