A powerful earthquake struck off the coast of northern Japan on Monday, triggering a tsunami alert, the Japanese Meteorological Agency said.

A powerful 6.8-magnitude earthquake struck Alaska late Saturday, according to the US Geological Survey (USGS).

The tsunami warning was issued for the prefectures of Hokkaido, Aomori and Iwate, after the quake jolted a large part of Japan's north and east at 11:15 p.m. (1415 GMT).

A Chinese carrier strike group sailing close to Japan kept up intense air operations on Sunday as it sailed into the Pacific Ocean east of the Okinawa Islands, Japan's Self-Defense Forces said Monday.