The US Geological Survey said the quake struck 219 kilometers south-southeast of Severo on the Kuril chain north of Japan. It was 56 kilometers (37 miles) deep.
The Pacific Tsunami Warning Center said hazardous tsunami waves were possible within 1,000 kilometers of the quake's epicenter.
It said earthquakes of this strength in the past have caused tsunamis far from the epicenter, and the US National Tsunami Warning Center was analyzing the event to determine the level of danger.