Around 5:45 a.m., new fire was discovered in northeastern corner of reactor 4 building, where an apparent hydrogen explosion caused a fire Tuesday morning following Friday's 9.0-magnitude quake.

Tokyo Electric Power Co. spokesman Hajimi Motujuku said the blaze erupted in the outer housing of the reactor's containment vessel. It was later confirmed that the fire was because the first blaze was not completely extinguished. Fire fighters are trying to put out the flames.

At the Fukushima Dai-ichi plant, there have been explosions at two reactor buildings since Friday's disasters.

Radiation levels around the Fukushima plant had "risen considerably", Prime Minister Naoto Kan said Tuesday, and his chief spokesman announced it had reached the point where it endangered human health.

In Tokyo, 170 miles (270 kilometers) to the southwest, authorities reported radiation levels nine times normal.

The National Police Agency said Tuesday that Friday's catastrophic quake and the ensuing tsunami have left at least 3, 373 people dead and 6,746 others unaccounted for in Japan.

*** On Tuesday evening, the magnitude of a strong and shallow earthquake which jolted Shizuoka Prefecture and its vicinity, including Tokyo, was revised upward to 6.4 from 6.0, according to the Japan Meteorological Agency.

The earthquake rocked eastern Honshu island at 10:31 p.m. local time (13:31 GMT), with a depth of 10 km, the U.S. Geological Survey said.

No tsunami warning was issued and no damage to the nuclear power plants were reported, Kyodo news agency said.

The quake came as Japan is struggling to tackle the aftermath of the catastrophic magnitude 9.0 quake and ensuing tsunami in the country's northeast last Friday.