Tsunamis of up to 15 inches were reported at four areas along the coast, although the advisory was lifted less than two hours after the quake, with no immediate reports of damage on land.
The quake hit at 2.10am Tokyo time on Saturday (5.10pm GMT on Friday) about 170 miles off Fukushima, and it was felt in Tokyo, some 300 miles away.
"It was fairly big, and rattled quite a bit, but nothing fell to the floor or broke. We've had quakes of this magnitude before," a government disaster management official said. "Luckily, the quake's centre was very far off the coast."
The operator of the troubled Fukushima Dai-ichi nuclear plant, Tokyo Electric Power, said no damage or abnormalities have been found so far. The plant was severely damaged in a 2011 earthquake and tsunami and has been shaken by a series of more minor tremors since then. Several plant workers near the coast preparing for a typhoon were ordered to evacuate to higher ground.
All but two of Japan's 50 nuclear reactors have been offline since the March 2011 earthquake.