At least four people are feared dead in Canada's Alberta Province and nearly 100,000 people have been forced to flee their homes after days of flooding.

Schools in Calgary city were closed and the military sent in a dozen helicopters and 1,200 troops to help clear more than two dozen neighbourhoods on Friday as heavy rains caused the Bow and Elbow Rivers in western Canada to overflow their banks.

Calgary Mayor Naheed Nenshi urged residents to gather their belongings and flee. He told them to expect to be away from their homes for a few days while police patrolled streets shouting evacuation orders over loudspeakers.

Electricity was cut in some parts of the city, and several roads and bridges were closed to traffic.

Firefighters swarmed residential neighbourhoods, carrying stragglers out of homes through knee-high waters or in boats to safety.

A large swath of centre of the city that includes the iconic Saddledome, home of the National Hockey League Calgary Flames, and surrounding lands where the city was to host its annual Stampede rodeo in just 15 days, was flooded.

Damage was said to be extensive.

State of emergency

Calgary resident Adam Klamar said all of the city centre was emptied of people by midday.

"It's pretty empty now," he said by telephone. "The whole downtown is on lockdown, they're not letting anyone in or out, there's only one or two routes still open."

"It's still raining," he said.

With more rain forecast over the weekend, water levels are expected to continue rising in the city of one million people that hosted the 1988 Winter Olympics, before cresting.

Twelve communities in surrounding Alberta Province meanwhile have declared a state of emergency, and mudslides forced the closure of the Trans-Canada Highway, isolating the mountain resort town of Banff.

Television footage showed swift currents carrying away cars and destroying homes in nearby towns.

Patients were also evacuated from two hospitals in Canmore and High River.

Prime Minister Stephen Harper was expected to tour the flood ravaged regions, which includes his electoral district in Calgary.