A Tsunami warning has been issued for coastal areas of Alaska and parts of Canada following an 8.2-magnitude earthquake.
Residents of Anchorage - population 300,000 - are being urged to get to higher ground amid warnings of an "extraordinary threat to life or property".
The earthquake struck at a depth of 6.2 miles at 9.31am GMT, the US Geological Survey said.
A tsunami watch is also in place for the whole US West Coast and Hawaii.
The Anchorage Office of Emergency Management warned those living in coastal areas of Alaska and British Columbia: "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."
Warning sirens are also ringing out across Kodiak, located about 157 miles northwest of the tremor's epicentre.
8.2 is a very strong quake. How much of a tsunami it generates will depend upon the type of fault that has produced it. The Japanese one has a massive shift in the height of the seabed.