A magnitude-6.6 earthquake struck off the east coast of Russia's Kamchatka at a depth of 10 kilometers on Sunday, according to the China Earthquake Networks Center (CENC).

It was followed by a series of strong earthquakes, with the major one measured at magnitude 7.2 in the same area, the CENC updated.

The U.S. Geological Survey issued a tsunami alert, warning that "hazardous tsunami waves are possible" within 300 kilometers of the epicenter in the Pacific, off the city of Petropavlovsk-Kamchatsky.

(With input from AFP)