A strong earthquake has struck off Japan, shaking buildings in Tokyo and triggering a small tsunami.

The tremor struck about 10 kilometres below the Pacific sea floor, about 160 kilometres off Japan's main island of Honshu.

The earthquake lasted for more than 30 seconds, swaying buildings in the capital, shutting down bullet train operations and triggering a tsunami warning.

A 60-centimetre surge was later recorded along coastal areas.

There were no reports of casualties or damage to buildings, with several nuclear power plants in the area given the all clear.

The 7.2-magnitude quake - which struck around noon (local time) in the northern part of Miyagi prefecture - measured a lower five on the Japanese seismic intensity scale of seven.

Earthquakes are common in Japan, one of the world's most seismically active areas.

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