An earthquake measuring 6.4 on the Richter scale hit Japan's northeastern Fukushima Prefecture and its vicinity on early Sunday Morning, said the Japan Meteorological Agency.

The focus of the quake, which occurred at 03:54 am local time was located some 40 kilometers under the sea off Fukushima, said the agency.

There were no immediate reports of casualties or damage to properties, and no tsunami warning was issued.

Strong tremors were felt in Tokyo, about 240 kilometers away from the prefecture. There have been no immediate reports of abnormalities from the quake by the operator of the troubled Fukushima No.1 nuclear power plant.