Flooding forced the evacuation on Friday of some 100,000 people in the western city of Calgary and nearby towns in the heart of the Canadian oil patch.

Schools were closed and the military sent in a dozen helicopters and 1,200 troops to help clear more than two dozen neighborhoods 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 neighborhoods, carrying stragglers out of homes through knee-high waters or in boats to safety.

A large swath of downtown 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.

Calgary resident Adam Klamar said all of the city's downtown 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."

He said he has seen the odd person walking around, and a few cars drive by, but otherwise the city center is eerily quiet, with only the sounds of sirens heard against a backdrop of rain coming down.

"It's still raining," he lamented. "It looks like it's getting worse... it seems to be raining more than it was this morning. "If it doesn't stop raining it could get worse."

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. However no injuries or deaths have been reported.

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, in the late afternoon.