A TSUNAMI alert was issued for Japan's northeast coast today after a powerful 7.3-magnitude undersea earthquake struck, setting buildings in Tokyo swaying violently.
There was no threat of a tsunami in the wider Pacific Ocean, according to the US-based Pacific Tsunami Warning Centre, but it warned an earthquake of that magnitude could generate a tsunami that can be destructive for local coastlines.
The epicentre was 10km beneath the seabed, and the warning said the tsunami could be as high as 2m.
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 5.40pm (7.40pm AEDT).
The US 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 50cm tunami was expected to hit the coast of Iwate at 5.40pm, Fukushima at 5.50pm, and Aomori and Ibaraki at 6pm.
Nuclear plant operator Tokyo Electric Power told AFP there were no reports of further damage at the crippled Fukushima nuclear plant.
