Firefighters battled a three-alarm blaze in southwest Calgary. (Erin Collins/CBC)

About 300 people are homeless after a major fire engulfed the top floor of a southwest Calgary condo building, sending plumes of black smoke over the city.

At its height on Thursday afternoon, the flames tore ferociously through the four-storey building as burning debris fell to the ground. The roof subsequently collapsed.

The fire began on the roof and was fanned quickly by strong winds. (Submitted by Steve Jones)

The fire, which began just before noon, required the efforts of about 50 firefighters, who were also battling strong winds, said Stephen Nicholl, a spokesman for the fire department.

The three-alarm blaze began in two suites on the top floor of the 159-unit building, said deputy fire chief Len MacCharles. No one was injured, as most residents were not home at the time, he said.

"With the strong winds that were blowing through the attic, the fire spread quickly," said MacCharles.

The wood-construction building had a sprinkler system, but MacCharles could not confirm if it was working.

"Our whole world is in there, I have nothing right now. I just lost everything I own," said a tearful Tiffany Hogan, standing outside the building.

Flames engulfed the building's top floor. (CBC)

Craig Iffla had come home from work sick when the fire began.

"I was home for maybe 10 minutes and then the alarm went off and I went to evacuate the building and I look back inside and the whole two units on the top floor looked like they were on fire," he said.

"The wind, it looked like, took the fire and started spreading it through the whole top floor."

Suzanne and Christopher Moule watched the fire from across the street. The couple live in the United Kingdom but owned a second-floor condo in the building with their daughter.

"My husband has leukemia which he was in remission from and just had a relapse. This was our last visit to Canada together," said Suzanne. "I was planning to live here after it was all over and now I have nowhere to come to."

She said they don't have high hopes for their unit. "We think it's just ruined with water and stuff. You can see the water just pouring out."

"It's just stuff. I mean stuff can be replaced; people can't. So as long as everyone is OK I'm not too concerned," said Troy Pachal, who moved in recently and has insurance.

Paramedics assessed 17 people who were released.

Nicholl said firefighters saved two dogs from the complex, and are looking for more trapped pets.

Police blocked off the neighbourhood and evacuated a nearby shopping centre and other homes as a precaution.

With files from Peter Akman