Residents in several low-lying communities in Calgary have been ordered to leave their homes due to heavy rains, floods and the potential of high river flows.

Evacuations from areas along the Elbow River were ordered for six communities: Mission, Elbow Park, Stanley Park, Roxboro, Rideau and Discovery Ridge. Those areas are being evacuated immediately, with Calgary police going door to door telling people to leave.

Residents are being encouraged to find shelter with family or friends for the next 72 hours minimum. Reception centres have been set up for those who cannot find places to go.

City officials have warned that the magnitude of the flood could be worse than that of 2005.

A state of emergency has been declared in Calgary and several other communities in Alberta .

Calgary activated the city's municipal emergency plan late Thursday morning, in anticipation of the heavy flows in the Elbow and Bow rivers reaching the city.

The city also opened its Emergency Operations Centre, where key personnel from city business units and external groups such as Enmax, Atco and Alberta Health Services gather to support front-line responders. It serves as the city's multi-agency command centre for large-scale emergencies.

The decision to launch the centre was made based on the potential severity of incoming high river flows in combination with expected heavy rainfall.

The city has begun to implement its flood response plans and is deploying sandbags and temporary dams at key locations.

In Longview, Alta., about 85 kilometres south of Calgary, near Longview, the RCMP searched for two adults in the rain-swelled Highwood River after their trailer became submerged.

Meanwhile, heavy rain also prompted officials in the mountain town of Canmore, about 100 kilometres west of Calgary, to declare a local state of emergency after the banks of a creek that runs through the community became unstable.

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About 40 homes were evacuated at 2 a.m. MT on Thursday when the banks of Cougar Creek were deemed unstable, Canmore Mayor John Borrowman said.

"The situation is actually bad and getting worse," he said. "Now some of the smaller creeks are starting to flood."

The evacuees were taken in at the town’s civic centre and at two local hotels.

Other residents are being alerted to be ready to move if necessary.

High River, about 70 kilometres south of Calgary, also declared a state of emergency early Thursday morning after the Highwood River started overflowing its banks.

All homes and businesses in the hamlet of Bragg Creek, 44 kilometres west of Calgary on the edge of Kananaskis Country, were ordered evacuated as the Elbow River surges over its banks. Power to the area has been shut off.

Just downstream, residents of the townsite of Redwood Meadows were told they should leave their homes and use northbound Highway 22 to get out of the area. Townsite administration manager Pat Evans said the water is higher than it was during the last big flood in 1995.

In southwest Alberta, parts of the Crowsnest Pass are being evacuated because of high water levels.

In Turner Valley, southwest of Calgary, a sour gas wellhead ruptured at the same time as the town dealt with fast-rising flood waters in the Sheep River.

Turner Valley Coun. Barry Williamson said the pipeline was struck by river debris, adding that an evacuation was ordered for residences in the area.

The rupture caused a release of sour gas containing hydrogen sulfide (H2S) — a colourless, flammable gas that smells like rotten eggs — but officials have said the risk is now contained. Air quality monitoring at the point of the rupture isn't detecting dangerous sour gas levels.