Officials in Japan have warned of an increased risk of a "huge" earthquake in the next week after a 7.7 magnitude quake struck off the north-east coast, triggering an evacuation order and warnings of 3m tsunami waves.

A tsunami has begun to hit Japan after a powerful earthquake struck off its northern coast.

The quake measured an 'upper 5' on Japan's seismic intensity scale -- strong enough to make it difficult for people to move around.