Tsunami warning for Alaska and entire US west coast after 7.9-magnitude earthquake at sea

A map from the US Geological Survey. The large red dot shows the quake's location.

*A powerful quake hit off the coast of Alaska in the early hours of Tuesday.
*People in coastal Alaska were warned to flee inland or to high ground.
*The entire US west coast was put on "tsunami watch," which is a lesser state of readiness than a tsunami alert.

The entire western coast of the United States, as well as Alaska and parts of Canada, were placed on tsunami watch after a massive earthquake hit off the Alaskan coast on Tuesday morning.

The US Tsunami Warning System alerted people in Alaska shortly before 1 a.m. local time after the 8.2-magnitude quake struck.

According to the US Geological Survey, the tremor hit 157 miles southeast of Chiniak, Alaska, at a depth of 25 km at 12.23 a.m. Alaska Standard Time (9.31 a.m. GMT).

The US Geological Survey put the magnitude of the quake at 7.9, revised down from an earlier figure of 8.2.

Alaska and parts of Canada were given tsunami warnings, the highest level of alert. The western US coast was put on the lesser level of "tsunami watch," according to the Reuters news agency.

People on social media posted screenshots of emergency warnings sent to their phones, telling them to "go to high ground or move inland"

A public warning from the Office of Emergency Management in Anchorage, Alaska's biggest city, 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."

It warned that the first waves could start hitting from 1.45 a.m., in the town of Kodiak.

A map from the tsunami warning system, posted on Twitter, showed the travel times for any potential waves. According to their estimates, any tsunami would take at least three hours to strike the lower 49 states.

This story is developing.