TOKYO: A tsunami alert was issued for Japan's northeast coast Friday after a powerful 7.3-magnitude undersea earthquake struck, setting buildings in Tokyo swaying violently.

Media reports said a one-metre-high wave could sweep ashore in Miyagi prefecture, an area badly hit by the March 2011 tsunami that devastated a large swathe of coast in the northeast, killing thousands.

Broadcaster NHK, quoting the national meteorological agency, said the tsunami is expected to hit at 5:40 pm (0840 GMT).

The United States Geological Survey measured the quake's magnitude at 7.3.

NHK said the Japan Meteorological Agency had issued a tsunami warning, one notch lower than a tsunami alert, for the Pacific coast of Iwate, Fukushima, Aomori and Ibaraki prefectures.

A 50-centimetre tsunami was expected to hit the coast of Iwate at 5:40 pm, Fukushima at 5:50 pm, and Aomori and Ibaraki at 6:00 pm.

Nuclear plant operator Tokyo Electric Power told AFP there were no reports of further damage at the crippled Fukushima nuclear plant.