Residents in the Pacific Northwest of the US and western Canada are bracing for potentially life-threatening floods as several days of heavy rain have swollen a number of rivers and tributaries.

On Thursday, the National Water Center reported heavy flooding along the Skagit and Snohomish rivers in the state of Washington that is expected to continue through Friday.

In Canada, major highways to Vancouver have been closed because of flooding, debris and the risk of avalanches.

There are evacuation orders in place for thousands of people in the US and Canada, and authorities have warned more rain is on the way.

In the US, the governor of Washington state, Bob Ferguson, declared a statewide emergency and estimated 100,000 residents could face evacuation orders.

The emergency declaration warned that rain and possibly snow at mountain elevations would exacerbate flooding conditions.

Governor Ferguson said there were no reports of fatalities, but warned residents the risk wasn't over yet.

"The flooding levels we're looking at are potentially historic in nature, so we just want to emphasise how serious the situation is," Ferguson said at a news briefing,

The Skagit River "will be cresting tomorrow mid-morning. Again, that is expected to be historic level on that river", he told CNN on Thursday evening.

He warned it would take "weeks" to recover from the storm, and appealed for help from the federal government.

An evacuation order was lifted in the Orting community south of Seattle, but Central Pierce Fire and Rescue cautioned residents to "remain vigilant into the evening".

"Remember, turn around don't drown," the department wrote on Thursday on X.

More than 30 highways were closed across the state, with closures also affecting commuters in the Seattle area.

The flooding has hit all of western Washington, as well as further south along the Oregon coast.

Skagit County, a major agricultural area north of Seattle, issued an immediate evacuation order to residents who live on the floodplain. Some 75,000 people would be evacuated from low-lying areas, officials said.

The National Oceanic and Atmospheric Administration said on Thursday the Skagit river would cause "severe near-record flooding from Rockport downstream through Sedro Woolley".

It warned of "deep and swift flood waters" especially in the Cape Horn, Hamilton and Thunderbird area.

Rescues are taking place around the state, involving inflatable boats and helicopters.

Seven-year-old Jocelyn Rosas choked back tears as she returned to find her home in a mobile home park underwater in Monroe, a city northeast of Seattle.

"The only clothes I've got are just my pyjamas," she told the BBC's US partner CBS News.

Her father, Jose Rosas, said the family moved about two months ago after his wife was diagnosed with cancer. The move was intended to save money for his wife's treatment.

"It's hard because we had to explain to her why we moved over here," Rosas said.

"And now it's gone," he said of their home.

The Snohomish County Sheriff's Office said in an overnight social media post that they had rescued "multiple" people by helicopter after they got trapped in their homes in Sultan, Washington, about 40 miles (65km) north-east of Seattle.

Officials said the Snohomish River was experiencing major flooding and "dancing with records" as water lapped against a local flood wall.

King County - which contains the city of Seattle - and Snohomish County officials have warned the road closures could last for several days.

At the town of Concrete, the high water mark upstream was below estimates, but authorities have warned people that record levels elsewhere were still possible.

Across the border in Canada's British Columbia, there are multiple evacuation orders and flood warnings.

City officials said the Nooksack River was expected to overflow its banks, and they anticipate flooding, though not as severe as in 2021, when it caused significant damage and five deaths in the province.

Most major highways to the Lower Mainland are now closed, according to the travel-information website Drive BC.

The US-Canada Sumas Border Crossing is also closed to commercial traffic.

The entire region, spanning parts of both the US and Canada, has received torrential rain from an atmospheric river - a phenomenon where water evaporates into the air and is carried by the wind and forms long currents that surge through the sky like rivers flow on land.

Forecasters have warned of another storm on Sunday.