Powerful earthquake strikes off southern Japan

The Japan Meteorological Agency said the quake on Thursday registered magnitude 7.1 and was centred in waters off the eastern coast of Japan's southern main island of Kyushu at a depth of 30km.

The quake most strongly shook Nichinan city and nearby areas in Miyazaki prefecture on Kyushu island. 

The agency said tsunami waves of up to 50cm were detected along parts of Kyushu's southern coast and the nearby island of Shikoku about a half hour after the quake struck. 

The tsunami advisory was lifted from most coastlines except those along the Miyazaki prefecture.

Seismologists at the agency held an emergency meeting to analyze whether the quake had affected the nearby Nankai Trough, the source of past devastating earthquakes. 

They later issued an assessment that the potential for a future quake in the area from Kyushu to central Japan is higher than previously predicted. 

The agency said it would continue to closely watch movements of plates near the Nankai Trough.

That does not mean there is an imminent danger of a big quake, but they urged residents on the coasts along the trough - which spans about 500km - to review their quake preparedness, University of Tokyo seismologist Naoshi Hirata, a member of an expert panel, told a joint news conference with JMA officials.

There is a 70 per cent to 80 per cent chance of a magnitude 8.0 or 9.0 quake stemming from the Nankai Trough within the next 30 years, Hirara said, adding Thursday's quake raised that probability even while the timing or exact location could not be predicted.

The Fire and Disaster Management Agency said three people were injured in Thursday's quake. 

Two of them fell down when the quake struck and another was hit by a falling object.

Chief Cabinet Secretary Yoshimasa Hayashi said officials were assessing possible injuries or serious damage, though none were immediately reported. 

He urged residents of the affected region to stay away from the coastline.

JMA Seismology Department official Shigeki Aoki warned that strong aftershocks could occur for about a week.