TOKYO (Reuters) - An earthquake with a preliminary magnitude of 6.9 struck deep under the seabed off the coast of Japan south of Tokyo on Tuesday, the Japan Meteorological Agency said.

The quake's epicentre was near the Ogasawara islands south of Tokyo, the agency said, adding that a tsunami warning had not been issued. The quake's preliminary depth was put at 480km below the seabed. There were no immediate reports of damage.

Earthquakes are common in Japan, one of the world's most seismically active areas, and a magnitude-8.5 quake struck the area around the chain of islands that run south from Tokyo last month. There were no reports of casualties or serious injuries.

Japan accounts for about 20 per cent of the world's earthquakes of magnitude 6 or greater.

On March 11, 2011, the north-east 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.