TOKYO - A 5.0-MAGNITUDE earthquake shook northern Japan on Tuesday but there were no immediate reports of casualties or damage, officials said.

The country's meteorological agency said there was no risk of a tsunami from the quake, which hit at 0013 GMT (0813am Singapore time).

The epicentre was about 50km below sea level in the Pacific Ocean off Fukushima prefecture, some 200km from Tokyo, according to the agency.

Around 20 per cent of the world's most powerful earthquakes strike Japan. -- AFP