Torrential rain in parts of British Columbia set off landslides on Sunday and Monday, choking off highways, trapping dozens of vehicles and prompting evacuations and flood warnings.
The heavy rainfall extended into the Pacific Northwest of the United States, including Washington State, where Gov. Jay Inslee issued a severe weather state of emergency on Monday night for 14 counties, making state money available to respond. The governor also instructed the state’s emergency management division, with the help of the Washington National Guard, to coordinate assistance to the affected areas.
Flooding prompted Interstate 5, a major roadway connecting the United States and Canada, to be closed in both directions in Bellingham, Wash., about 24 miles south of the border, Washington’s transportation department said.
Residents of Merritt, a Canadian city of more than 7,000 people about 170 miles northeast of Vancouver, were told on Monday to leave their homes immediately after heavy rain caused the Coldwater River to spill its banks. The city announced that barricades would be erected to prohibit access to the city after 4 p.m. Monday.
Flooding then disabled the city’s waste water system, a municipal notice said, warning that anyone who stayed faced a “risk of mass sewage backup” that could threaten their health.
“Merritt residents cannot use any water, including running faucets and flushing toilets,” British Columbia’s minister of public safety, Mike Farnworth, said at a news conference on Monday.
Merritt officials said floodwaters had also inundated two bridges that spanned the river, which flows for 59 miles from the Cascade mountain range, and overwhelmed a third bridge, making it impassable.
As of Monday afternoon, there had been no confirmed reports of fatalities from any accidents related to the severe weather, Mr. Farnworth said.
“To the people of Merritt, and to all British Columbians affected by the flooding: please stay safe,” Prime Minister Justin Trudeau said on Twitter on Monday. “We’re ready to provide whatever assistance is needed as you deal with and recover from the flooding and this extreme weather.”
Bill Blair, the minister of emergency preparedness, said the government was “closely monitoring” conditions in southern British Columbia.
In Agassiz, a small community east of Vancouver, Mayor Sylvia Pranger declared a state of emergency after a landslide occurred and a flood watch warning was issued for the District of Kent, which includes Agassiz. The landslide blocked traffic along two roadways, officials said: Rockwell Drive, stretching about 1.5 miles, and the Lougheed Highway, which runs for about 95 miles and is also known as Highway 7.
Martina Martinkova, who was driving with her daughter on that highway near Agassiz, spent more than half a day in her car, which was one of at least dozens of vehicles brought to a standstill by the muck.
“Many people” in the area were rescued by helicopter on Monday, Mr. Farnworth said, without providing exact numbers.
In an interview aired by the Canadian Broadcasting Corporation, Ms. Martinkova, sitting in her dark car with her child peering over her shoulder from the back seat, said people in vehicles around her were sharing food and water throughout the ordeal.
“We were very lucky it didn’t hit us,” she said of the landslide, adding that the group had fruit and Coke. “It is very scary.”
Paul Doel, who became trapped with his family in a pickup on Sunday night because of two mudslides north of Hope, British Columbia, told the CBC that he and other stranded motorists had “built a little bit of a community.”
He said that at the largest of the two slides, “it looks like the side of the mountain has just come apart,” leaving a huge pile of debris along a large stretch of the highway.
On Sunday, before he became stuck, Mr. Doel said that the heavy rain had washed out several sections of the highway and created deep potholes that destroyed the tires of several vehicles.
About 150 people were trapped in Mr. Doel’s group, he said, including health care workers and a highway department crew member. Despite the long hours without word from the authorities, he said no one had panicked. “We’re just hanging out,” he said, adding: “We’ve got internet so that’s saving a lot of people.”
Mr. Farnworth told reporters on Monday that about 80 to 100 vehicles had become trapped on Highway 7, and that emergency workers had rescued many people in the area, adding that exact numbers were being assessed.
“Progress had been made,” he said. “We’ve heard from people who are concerned about their loved ones being in their vehicles and trapped on these slides. We hear you, and we know it’s difficult. But help is on the way.”
Mr. Farnworth said Monday afternoon that crews were working to rescue “the remaining people” in Agassiz and Hope over the next few hours.
On Monday afternoon, a Royal Canadian Air Force squadron was assisting with the rescue efforts using helicopters.
The weather system was caused by an atmospheric river, part of a convergence of storms that was so vast that it swept from California into Washington and southern British Columbia.
In Washington, heavy rains caused flooding across parts of the state on Monday, including in the city of Forks, in a northwest corner of the state, where helicopter crews were needed to evacuate 10 people from a residential area, according to the U.S. Coast Guard of the Pacific Northwest.
In Whatcom County, in a northern part of the state that borders Canada, flooding prompted rescue operations, according to the Whatcom County Sheriff’s Office, and a mudslide shut down part of Interstate 5, according to the Washington State Patrol.
Justin Pullin, a meteorologist with the National Weather Service Seattle, said the region has experienced a “really wet fall this year.”
This week, the region was under a “long-duration rainfall event,” resulting in saturated grounds that, combined with the strong winds, have made bluffs unstable.
The severe weather comes after weeks of wildfires in the region. The authorities have warned that areas where vegetation has been shorn by fires could become susceptible to streams of rushing mud during heavy rains. Merritt had experienced record high temperatures and wildfires during the summer.