Authorities in Merritt, some 200 km (124 miles) northeast of Vancouver, ordered the 7,100 citizens to leave after rising waters severed bridges and forced the sewage treatment plant to close.
“The continued habitation of the community without sanitation presents a risk of massive backflow of sewage and a risk to personal health,” the city said in an official notice.
Some areas received 200mm (8 inches) of rain on Sunday – the amount they usually see in a month – and the flood continued on Monday, with roads covered in mud or up to 250mm (10 inches) of water.
“The heavy rains and subsequent mudslides / flooding impacted various highways in the interior of British Columbia,” the BC Ministry of Transportation said on Twitter.
Storms forced the closure of the Trans Mountain pipeline, which carries crude from Alberta to the Pacific coast. The line has a capacity of 300,000 barrels per day.
Work on a proposed expansion project has also been halted, the operating company said.
Rescuers have been deployed to free people trapped for hours in 80 to 100 cars and trucks between mudslides near the town of Agassiz, provincial Security Minister Mike Farnworth said during a press conference.
People may need to be evacuated by air, he said, although high winds could “jeopardize these efforts.”
“The side of the mountain has just collapsed,” the stranded motorist Paul Deol told the CBC.
Farnworth said there had been “multiple incidents caused by the rain” in the southwest and central areas of the province, calling the situation “dynamic”.
“The weather is very difficult.
About 29 km (18 miles) further east, footage posted to Facebook showed parts of a road washed away near the town of Hope.
In the town of Abbotsford, outside of Vancouver, authorities have ordered the evacuation of more than 100 homes in several neighborhoods threatened by flooding and mudslides.
Gales are expected to hit the area later, most likely causing power outages, officials said.
The storm is the second weather calamity to hit the Pacific province in just a few months. At the end of June, temperatures reached an all-time high, killing more than 500 people and causing fires that destroyed a city.