Dangerous conditions include "extreme waves, storm surge, hurricane force wind gusts, coastal erosion and heavy rainfall," US weather agency NWS says.
A historically powerful storm is hammering western Alaska, causing huge tidal surges and flooding that has torn some houses from their foundations, US weather forecasters said.
The remnants of Pacific Typhoon Merbok have created one of the strongest storms to impact the region at this time of year in decades and are expected to batter the coast throughout the weekend.
Dangerous conditions include "extreme waves, storm surge, hurricane force wind gusts, coastal erosion and heavy rainfall," the National Weather Service said on Twitter on Saturday.
"Flooding will get worse," the service's Fairbanks, Alaska office tweeted.
There were no immediate reports of injuries or deaths Governor Mike Dunleavy said as he declared a disaster for impacted communities.
"This is easily the strongest storm this early in the autumn in the past 50 years in the Bering Sea," Rick Thoman, a climatologist at the University of Alaska-Fairbanks, told the AFP news agency via email.
In the coastal village of Golovin, the Fairbanks office said, "water is surrounding the school, homes and structures are flooded, at least a couple homes (are) floating off the foundation."
'A very angry sea'
Images on social media showed considerable damage. Footage on CNN showed one house floating down a river before being wedged under a bridge.
The NWS described "a very angry sea" along the coast around Nome, with a tidal surge approaching 3.3 metres, the highest since a 1974 flood.
Wind gusts as high as 145 kilometres per hour have been recorded, the NWS said, with stronger gusts expected later.
The NWS office in Anchorage reported seas of up to 41 feet late Friday.
Analysts were describing the storm as of historic dimensions.
"There has been extensive damage from flooding and high winds at numerous communities along the west of Alaska. This includes damage to homes and other buildings (and) flooding of airports," Thoman said.
With the storm on a northward track, flood warnings remain in effect until 10:00 pm Saturday (0600 Sunday GMT) in southern coastal areas and until 8:30 am Sunday in northern regions, NWS officials said in a briefing on Facebook.