Winnipeg's fire and police resources fought a major fire at an East Elmwood roofing-supply company Thursday night. (CBC)Winnipeg firefighters battled a massive and stubborn fire that sent potentially toxic smoke billowing out over the East Elmwood neighbourhood Thursday.

Police said the fire at SPAR-Marathon Roofing Supplies at Kent Street and Thomas Avenue was called in at 7:34 p.m. local time and kept burning for hours.

Emergency crews and police at the scene had their hands full trying to keep spectators away from the area as propane tanks stored near the scene were in danger of exploding.

Police also warned spectators the smoke from the burning roofing materials could be toxic.

Patrons and employees of several nearby businesses were ordered evacuated by police as a precaution. However, residents of homes about a kilometre away were not told to leave, a police spokesman said.

It was not immediately known if there were any injuries. Fire officials were unavailable to comment on what may have started the blaze or offer a damage estimate.

The entire area of East Elmwood was enveloped in a haze of thick smoke.

Onlookers watch fire crews as they try to put out the major East Elmwood blaze. It's unknown if anyone was injured. (CBC)One area resident, Rajdeep Dhaliwal, said he pulled his car over to get out and watch. But he said he dared not get too close.

"It was just smoke first, then explosion," Dhaliwal said. "And that wall in the corner there fell down and [there was] a whole bunch of smoke in the sky."

An employee of the business, Brent Phimister, told CBC News that gas tanks on small forklifts used to carry heavy materials from place to place inside the business likely caused the explosion.

Phimister said there were many potentially flammable objects at the store that may have fuelled the fire.

“There's a lot of roofing supplies, there's shingles in the yards, there's a few flammables,” Phimister said.

The major traffic artery of Nairn Avenue between Chester Street and Stapleton Street remained closed late Thursday.

Motorists were advised to avoid the area.

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