Calgary fire crews gained control of a stubborn fire at the Stadium Shopping Centre in the northwest that sent plumes of black smoke into the air for several hours on Thursday.

Crews were called to the strip mall at 16 Avenue and Uxbridge Drive NW at about 7:20 a.m. after flames were spotted on the roof by a passerby.

"We came to work this morning, I opened, and all of a sudden I saw the fire truck come around so I went around to the back, I seen some smoke and came back around to the front and that was it. All the fire trucks showed up," said one woman.

Officials believe the blaze began at Billingsgate Seafood Market and Restaurant and then spread to neighbouring stores.

Firefighters sprayed water on the fire from above and used thermal imaging equipment to monitor for flare ups.

Peter Chao, with the Cat House, one of the businesses in the strip mall, says crews helped to rescue cats from the store. "The fire guys got the cats out, so they're safe - a bit spooked - but they've been relocated with some water so I'll keep an eye out for them and hopefully they'll be 100 percent soon."

Carol Henke, public information officer with the Calgary Fire Department, told CTV News that the fire was contained to the one business.

"There are no injuries at this time," said Henke. "We have thermal imaging cameras to see where the heat is concentrated so we can find the seed of the fire."

Several trucks were called to the scene and officials say it was because they had no idea how large the fire was when they got there. "Even small fires can produce a lot of smoke. We would rather err on the side of caution, have more apparatus and then return them to their stations when they are not needed," said Henke.

Two schools were evacuated as a precaution. Early Thursday evening, the Calgary Board of Education announced Friday's classes at the University School have been cancelled due to air quality issues in the neighbourhood.

The mall was built in the 1960s and is slated for demolition next year to make way for a new mixed-use development. The age of the facility made it challenging for firefighter to control the blaze.

"The issues we're running into is the roofing material itself, which is a combination of drywall, straw, tar and metal and the fire has gotten in between the layers of the straw and has started to move around the building itself," said CFD Battalion Chief Al Magwood.

Fire officials say six businesses were damaged in the fire and two firefighters were taken to hospital for injuires sustained while fighting the blaze.

A Track Hoe has been brought in to bring down the damaged parts of the building so fire crews can gain better access.

The cause of the fire is not yet known and is under investigation.

The Calgary Fire Department is asking anybody has information, photos or video regarding today's fire, please email them to piofire@calgary.ca