The magnitude 6.8 quake struck at 6.12 am (local time) at a depth of 46 kilometres off the coast of Miyagi prefecture, the Japan Meteorological Agency said.

It shook a wide swath of northern Japan and was felt in Tokyo, 415 kilometres to the southwest. There were no immediate reports of injuries or damage.

Meteorological agency official Yohei Hasegawa told a news conference that the earthquake was an aftershock of the magnitude 9.0 disaster that killed more than 18,000 people in March 2011.

No abnormalities were reported at the Fukushima Dai-ichi nuclear power plant, which was damaged beyond repair in the 2011 disaster, or at other reactors in the region.