A moderate earthquake with a preliminary magnitude of 5.6 jolted an area south of Tokyo today, the Japan Meteorological Agency said.
The quake was felt in Tokyo, but there were no immediate reports of damage, and no tsunami warning was issued.
The focus of the tremor, which struck at 6.24pm (10.24am Irish time), was 20 kilometres below the ocean floor off the Izu Peninsula in Shizuoka prefecture, about 80 kilometres southwest of Tokyo, the agency said.
Some train services, including bullet trains in the area, were briefly halted as a precaution.
Earthquakes are common in Japan , one of the world's most seismically active areas. The country accounts for about 20 per cent of the world's earthquakes of magnitude 6 or greater.
In October 2004, an earthquake with a magnitude of 6.8 struck the Niigata region in northern Japan, killing 40 people and injuring more than 3,000.
That was the deadliest quake since a magnitude 7.3 tremor hit the city of Kobe in 1995, killing more than 6,400