The quake hit 300 km southeast of Kodiak at a depth of 10 km at 12.21 a.m., the US Geological Survey said.
The US National Tsunami Warning Centre issued a tsunami alert for areas that included the coast of Alaska to British Columbia and the border with Washington State, and a tsunami watch all the way down to the border of Mexico and the coast of Hawaii, the New York Times reported.
Anchorage, Alaska's largest city, issued an extreme warning, saying there was "extraordinary threat to life or property".
The alert told people to seek refuge on higher grounds in affected areas. Authorities said that based on the preliminary earthquake parameters, "widespread hazardous tsunami waves were possible".
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