Pakistan, July 21 -- A series of powerful earthquakes struck off the coast of Russia's far east on Sunday, triggering a tsunami alert, the US Geological Survey said.

Earlier 5.0-magnitude and 6.7-magnitude earthquakes did not initially trigger a tsunami alert, but were followed by a 7.4-magnitude quake at 0849 GMT (1:49pm PKT), prompting the USGS to warn that "hazardous tsunami waves are forecast for some coasts".

The USGS said it expected waves of between 30 centimetres and one metre (up to 3.3 feet) on Russian coasts, and less than 30cm (one foot) in Japan and the US state of Hawaii.

The epicentre of the quakes was in the Pacific Ocean, around 150 kilometres east of the city of Petropavlovsk-Kamchatsky, it said.

The initial earthqua...