The Alaska earthquake struck 157 miles south-east of Chiniak, at 9.31am GMT (12.31am local time) on Tuesday, January 23.
The Alaska earthquake prompted a tsunami warning for parts of Alaska and Canada and a tsunami watch for the entire US West Coast, the US Tsunami Warning System said.
The NWS Pacific Tsunami Warning Center said that, based on the preliminary earthquake parameters, “widespread hazardous tsunami waves were possible”.
A shocking video reveals the huge scale of the tsunami warning, with rings spreading across the Pacific Ocean as a result of the tremors.
The quake had a depth of around six miles, according to USGS.
It is already expected to be one of the largest quakes in US history.
Details on damage and casualties have not yet emerged.
Alaska is situated on the Ring of Fire, a huge area in the basin of the Pacific Ocean where earthquakes and volcanic eruptions frequently occur.
A buoy has recorded a wave of 10-metres (32ft) just northeast of the epicentre of the Alaska earthquake
Experts suggest the first waves could start hitting from 1.45 am, in the town of Kodiak.
A map from the tsunami warning system 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.
Only four earthquakes with a greater magnitude have ever been recorded in the USA.
And all of them were in Alaska, causing a tsunami on each occasion.
The most powerful earthquake was on March 27, 1964, when a 9.2 magnitude quake killed 139 people.