A strong 6.5-magnitude earthquake struck beneath the sea off Papua New Guinea on Monday, Photo: AFP

The focus of the tremor was 20 km (12 miles) below the surface of the earth, in Yamanashi prefecture, west of Tokyo, the Japan Meteorological Agency said.

The quake, at 7:43 a.m., was also felt in the capital.

Earthquakes are common in Japan, one of the world's most seismically active areas. The country 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, which triggered the world's worst nuclear crisis in 25 years since Chernobyl. The disaster left up to 23,000 dead or missing.