TOKYO - An earthquake measuring 5.8 on the Richter scale shook northern Japan early Tuesday but there were no immediate reports of damage, meteorological and municipal officials said.

The quake struck at 2.10 am (1710 GMT) off the coast of Hokkaido prefecture, with the epicenter located 1,050 kilometers north of Tokyo and 50 kilometers below sea level, the meteorological agency said.

There was no risk of tsunami waves, it said.

'We have got no reports of injuries or damage,' a local disaster-prevention official said.

Japan, which experiences about 20 percent of the world's major quakes, introduced a world-first early warning system for earthquakes but the latest tremor was not big enough to activate the system.