A powerful earthquake struck off Japan's southern coast on Thursday, triggering a tsunami advisory that urged residents to stay away from the coastline. Three people were injured but there were no reports of serious damage.
The Japan Meteorological Agency said the quake 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 about 30 kilometres (18.6 miles).
The quake most strongly shook Nichinan city and nearby areas in Miyazaki prefecture on Kyushu island.
The agency said tsunami waves of up to 50 centimetres (1.6 feet) 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 analyse 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 will continue to closely watch movements of plates near the Nankai Trough.
That does not mean there's an imminent danger of a big quake in the near future, but they urged residents on the coasts along the trough -- which spans about 500 kilometres (310 miles) -- 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 70-80% chance of a magnitude 8 or 9 quake stemming from the Nankai Trough within the next 30 years, Hirara said, adding that Thursday's quake raises that probability even while the timing or exact location cannot 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.
Japan's NHK public television said windows were broken at the Miyazaki airport near the epicentre. The airport's runway was temporarily closed for safety checks.
NHK showed dozens of people gathering at a designated hilltop evacuation area.
In Osaki in neighbouring Kagoshima prefecture, concrete walls collapsed and a wooden house was damaged, but no injuries were reported.
The Nuclear Regulation Authority said all 12 nuclear reactors, including three that are currently operating, on Kyushu and Shikoku remained safe.
Earthquakes in areas with nuclear power plants have been a major concern since a massive earthquake and tsunami in March 2011 triggered the Fukushima nuclear disaster.
Japan sits on the Pacific “Ring of Fire", a line of seismic faults encircling the Pacific Ocean, and is one of the world's most earthquake-prone countries.
An earthquake on Jan. 1 in Japan's north-central region of Noto left more than 240 people dead.
