The U.S. Geological Survey said the quake struck 219 kilometers south-southeast of Severo on the Kuril chain far 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 (600 miles) of the quake's epicenter.
It said earthquakes of this strength in the past have caused tsunamis far from the epicenter. A tsunami watch was issued for Hawaii but the center said it was still investigating if there was a threat to the islands.
The U.S. National Tsunami Warning Center also still was analyzing the event to determine the level of danger for Alaska and the U.S. West Coast. The Japan Meteorological Agency said the quake was a stronger 7.8 magnitude and may cause a slight change of sea levels around Japanese coasts.