TOKYO (Reuters) - There were no immediate reports of damage after northern Japan was hit by an earthquake which the Japan Meteorological Agency said had a preliminary magnitude of 6.8.

The epicenter of the quake was in the Pacific Ocean off the coast of northern Japan, the agency said, adding that a tsunami warning for a wave with an estimated height of 50 cm had been issued.

On March 11, 2011, the country's northeast coast was struck by a magnitude 9 quake, the strongest 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.

(Reporting by Tokyo news room; Editing by Joseph Radford)