The focus of the quake, which occurred at 03:51 a.m. local time was located some 40 km 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. Tremors were felt in Tokyo, about 240 kilometers away from the prefecture.

There was no immediate reports of abnormalities from the quake by the operator of the crippled Fukushima No.1 nuclear power plant.