By David Ljunggren

OTTAWA (Reuters) -Massive rainstorms lashed the western Canadian province of British Columbia on Monday, triggering landslides and floods, shutting highways and prompting the evacuation of an entire town.

Authorities in Merritt, some 124 miles (200 kilometers) north east of Vancouver, ordered all 8,000 citizens to leave after rising waters cut off bridges and forced the waste water treatment plant to close.

“Continued habitation of the community without sanitary services presents risk of mass sewage back-up and personal health risk,” the city said in an official notice.

Some areas received 8 inches (200 mm) of rain on Sunday – the amount they usually see in a month – and the deluge continued on Monday, with roads covered by mud or up to 10 inches of water.

Landslides trapped the occupants of between 80 and 100 vehicles near the mountain town of Agassiz, about 120 km east of Vancouver, and people may have to be airlifted out, a top official said.

“The side of the mountain has just come apart,” stranded motorist Paul Deol told the Canadian Broadcasting Corp.

Around 18 miles further east, footage posted to Facebook showed parts of a road had been washed away near the town of Hope.

“The situation is dynamic … it is very difficult weather,” provincial public safety minister Mike Farnworth told reporters.

Gales are due to hit the area later, most likely causing power outages, officials told reporters.

The storm is the second weather-related calamity to hit the Pacific province in just a few months. In late June, temperatures hit a record high, prompting blazes that destroyed one town.

(Reporting by David Ljunggren; Editing by Aurora Ellis)