A tsunami alert has been issued for the west coast of America after a powerful 8.2-magnitude earthquake struck off Alaska.

The quake hit 157 miles south east of the town of Kodiak at about 9.30am GMT on Tuesday (12.30am local time). It was in the Gulf of Alaska at a depth of 6.2 miles (10km), the US Geological Survey reported.

The earthquake prompted a tsunami warning for coastal Alaska and the west coast of British Columbia in Canada. Less severe tsunami watches were issued for the US west coast – the entire coasts of California and Oregon and part of Washington state.

Anchorage, the largest city in Alaska, issued an extreme warning, saying there is “extraordinary threat to life or property”. The alert told people living on the coast to “go to high ground or move inland”. A map issued by the US National Tsunami Warning Center showed the at-risk areas.

People reported on social media that the quake was felt hundreds of miles away in Anchorage.

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The Anchorage Office of Emergency Management said, “If you are located in this coastal area, move inland to higher ground.”

“Tsunami warnings mean that a tsunami with significant inundation is possible or is already occurring. Tsunamis are a series of waves dangerous many hours after initial arrival time. The first wave may not be the largest.”