Up to 100,000 people could be forced from their homes by heavy flooding in western Canada, with mudslides forcing the closure of the Trans-Canada Highway and cutting off the mountain resort towns of Banff and Canmore.
Torrential rain and flooding in southern Alberta on Thursday washed out roads and bridges.
At least one person was reported missing.
Communities just south of Calgary were hit hard, with many neighbourhoods evacuated as the evening went on.
Officials said the evacuation would take place in stages over the next few days. The province reported that 12 communities were under states of emergency.
One woman stranded on top of a trailer was missing after it was swept away, air ambulance spokesman Cam Heke said.
Motorists who were trapped overnight on Wednesday by water spilling over Canada's main western highway had to be rescued by helicopter, Town of Canmore spokeswoman Sally Caudill said.
"I woke up at about three o'clock in morning to the sound of this kind of rumbling, and it was the creek," said Wade Graham, a resident of Canmore.
"At first it was just intense, pretty powerful, an amazing thing to watch. As daylight came, it just got bigger and bigger and wider and wider."
He added, "I watched a refrigerator go by. I watched a shed go by. I watched couches go by. It's insane."
In High River, Mounties asked people with motorboats to help rescue at least a dozen stranded homeowners.
Bruce Burrell, director of the Calgary Emergency Management Agency, said water levels on the Bow River were not expected to subside until later. The Bow River Basin has already been battered by up to 100mm of rain.
Environment Canada issued a rainfall warning for the affected areas, estimating as much as 100mm of more rain could fall in the next two days.