A major wind storm blowing through southern Alberta forced Calgary to close its downtown area to traffic, and led to evacuation orders for homes on the outskirts of Lethbridge threatened by grassfires.

The Calgary Fire Department recorded wind gusts of up to 149 kilometres per hour atop highrises in the city, which accounted for blown-out windows and other damage to buildings.

Reports of damage came from all areas of Calgary. In the west end, winds tore the roof of a home, while at the central TD Square shopping centre, shards of glass from several broken windows crashed into a vehicle.

Trees toppled over onto power lines, leaving thousands of city residents without power for several hours.

"Right now, there's just so much stuff falling off buildings that we're struggling to keep up with calls," Det. Dean Vegso of the Calgary Police said Sunday afternoon.

Police asked residents to stay inside their homes.

"Put as many walls between you and the storm as possible," reads a critical alert issued by the City of Calgary. "Seek shelter. Watch out for flying debris. Stay away from downed powerlines and trees that may fall. Please dial 911 only if you have an emergency."

Parks were closed to the public on Sunday, while public transportation was shut down.

Meanwhile, officials asked residents who live in Lethbridge County, west of the city, to leave their homes and businesses because of a grassfire burning west of Lethbridge.

The province's Emergency Management Agency issued the evacuation order on Sunday evening, and pointed residents to a reception centre at the Fritz Sick Centre.

The agency also warned residents of West Highlands and Indian Battle Heights to be prepared to leave their homes because of a grassfire in that area.

The city of Lethbridge also asked residents to reduce their cellphone use, and only use phones for emergency calls.

In High River, residents were told to leave an apartment building after officials found that a fire wall had separated from the building.

High winds also wreaked havoc on the roads. RCMP urged drivers to avoid travelling on Highway 2 between Nanton and Fort Macleod, and in the areas surrounding Fort Macleod and Claresholm.

One image sent to MyNews showed a semi-truck blown onto its side along a highway near Airdrie, just north of Calgary.

"It's a lot more severe out in the country where there isn't anything to block the winds when it's coming across the fields," Jillian Millar, who drove south from Calgary on Sunday afternoon with her husband, told The Canadian Press.

"We didn't realize it was as bad as it was when we left the house," she added.

Alberta's emergency alert system had been activated and was broadcasting a warning on the radio to warn residents to stay away from windows.

Environment Canada said the high winds were caused by "a strong pressure gradient" that developed over the region "as a result of a low pressure system that has moved into Southern Northwest Territories."

With a report from CTV Calgary