A tsunami alert has been issued after a 7.4-magnitude earthquake in the Pacific Ocean off southern Japan, the US Geological Survey (USGS) says.
The epicentre of the earthquake was 155km (95 miles) off the Bonin Islands, some 1,000km south-east of Tokyo, the USGS said.
It struck at a depth of nearly 15km, the agency added, at around 0220 (1720GMT).
Japan is well-prepared for quakes which often hit the seismically active area.
In 1995, a magnitude-7.2 quake in the port city of Kobe killed 6,400 people.
There were no reports of casualties or damage in the latest earthquake, but a mild tsunami warning was issued for nearby islands.
Japan's meteorological agency warned the quake could cause waves about a metre (3.3ft) high, and local TV broadcasts warned coastal inhabitants to seek safety on higher ground.
Known in Japan as the Ogasawara Group, the Bonin archipelago comprises some 30 tropical or sub-tropical islands, only two of which are populated.
They are inhabited by around 2,500 people.