A magnitude-7.9 earthquakedetected in the Gulf of Alaska has triggered tsunami warnings in Alaska and tsunami watches across several Western states.
A tsunami warning is in effect for southeast and south Alaska, including the Alaska Peninsula and Aleutian Islands, as well asBritish Columbia in Canada. A tsunami watch is in effect for California, Oregon and Washington, according to the Tsunami Warning Center.
As of 2:29 a.m. (6:29 a.m. ET), water in the harbor near Kodiak was receding, the city's police department tweeted, after earlier urging residents to get at least 100 feet above sea level.
"Citizens should remain in place and wait for further updates," Kodiak police said.
The San Francisco Department of Emergency Management warned residents within three blocks of the Pacific Coast or within five blocks of the San Francisco Bay to prepare to evacuate, "so that you are ready if evacuation is needed," the agency tweeted.
The earthquake struck about 175 miles southeast of Kodiak, Alaska, shortly after midnight Alaska local time, according to preliminary figures from the United States Geological Survey. The quake had a depth of about 15 miles, according to the USGS. Previously, the earthquake had been measured at magnitude 8.2.
'Whole town is evacuating'
Nathaniel Moore was on a boat in Kodiak when the quake hit. He said he felt it "shake really good for a minute." He and others on the commercial fishing vessel quickly got to shore and headed for higher ground amid the tsunami warning.
"The whole town is evacuating," he told CNN early Tuesday.
Tsunami sirens sounded in Kodiak, and police warned: "This is not a drill."
Wendy Bliss Snipes described the quake as "a slow roller, so it was felt for at least a minute before the real rolling started. Nothing fell off the walls, and I didn't have to wake my kiddo."
tsunami sirens going off in kodiak after the earthquake, i usually only ever hear the weekly siren test at 2pm on wednesdays so hearing it at 1am on tuesday is actually terrifying!! pic.twitter.com/ea5y7U6xnf
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.
People in areas at risk from the tsunami threat have been warned of the dangers by text message.
Those in affected areas have been urged to seek high ground.
In a warning for Alaska and British Columbia, 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.”
Japan's meteorological agency said it was monitoring the situation but has not issued a tsunami alert.