There were no immediate reports of injuries or damage and no tsunami warning was issued. The U.S. Geological Survey measured the quake with a magnitude of 6.5.
The quake was measured 400 km (250 miles) below the earth's surface about 580 km (360 miles) south of Tokyo, NHK said. Witnesses said it was felt along much of Japan's east coast.
Earthquakes are common in Japan, one of the world's most seismically active areas. Japan accounts for about 20 percent of the world's earthquakes of magnitude 6 or greater.
On March 11, 2011, the northeast coast was struck by a magnitude 9 earthquake, the strongest quake in Japan on record, and a massive tsunami. Those events triggered the world's worst nuclear crisis since Chernobyl a quarter of a century earlier.