An earthquake measuring 6.0 on the Richter scale hit Japan's Fukushima Prefecture and its vicinity on early Friday morning, said the Japan Meteorological Agency (JMA).
The focus of the quake, which occurred at 03:22 a.m. local time, was located some 50 kilometers under the sea off the prefecture, said the agency.
There were no immediate reports of casualties or damage to properties, and no tsunami warning was issued.
Strong tremors were also felt in Tokyo. There have been no immediate reports of abnormalities from the quake by the operator of the troubled Fukushima No.1 nuclear power plant in the northeast prefecture.