A 7.0-magnitude earthquake has struck in seas off far northern Japan and far eastern Russia, but no damage was expected.
The Japan Meteorological Agency said sea changes were possible. No tsunami warnings have been issued.
The tremor struck in the Pacific Ocean at a relatively shallow depth of 6.2 miles. The US Geological Survey measured a stronger 7.2 magnitude.
Japan and Russia both claim some of the sparsely populated islands in the remote region.
The epicentre was 160 miles east-north-east of Kuril'sk, Russia, and 328 miles north-east of Nemuro, Japan.
The nearest land is the volcanic islands of Urup, Iturup and Sumushir. Hokkaido officials said the islands were not under Japanese control.
The area is about 930 miles north-east of Tokyo.