Firefighters continue to battle a massive six-alarm blaze - the highest rating used by Toronto's fire department - that is burning at a factory near Dufferin Street and Eglinton Avenue West.

Parts of the roof and walls collapsed in the inferno and firefighters are staying outside the industrial building because it is unsafe to enter and no one is believed to be inside.

“It’s just too dangerous to go in. There’s nothing to save, other than the contents,” said Toronto Fire Services Deputy Chief Mike McCoy. “As we get a handle on (the fire) on one end it basically ... runs to the other side of the building."

There are no reports of injury.

About 85 firefighters remained on scene as of 4 p.m., down from the 120 who were on-scene to battle the blaze at its height.

People who live in the area are being asked to keep their windows and doors closed because a huge wall of potentially-toxic smoke was drifting across part of the city.

At least four buildings in the immediate area were evacuated and at least nine schools were "sheltering in place" as a precaution, meaning they were keeping students inside for recess, turning off ventilation systems and keeping windows closed.

Police and school officials lifted that order around 4 p.m. and said schools in the area would be dismissed normally for the day.

The plume of dense, acrid smoke was visible from far away locations, including the city's waterfront, which is about 11 kilometres from the scene, and it was picked up on local radar.

Crews have been battling the stubborn fire on Fairbank Avenue, north of Castlefield Avenue, since 8:30 a.m. The large building is occupied by at least one company. That company produces foam and other materials used to make home furniture and mattresses.

Smoke was pouring out of the building when firefighters arrived, but flames were soon cutting through the roof as the blaze quickly spread.

The situation went to a sixth alarm at about 11:30 a.m., as 30 fire trucks and 120 firefighters tried to gain the upper hand. By then, the fire had spread to most of the crumbling structure.

Because of the scale of the fire, crews had to use a tremendous amount of water. The water pressure was low on some hydrants, so firefighters ran hoses from hydrants a few blocks away.

With most of the roof collapsed, fire officials said they may eventually have to bring in machinery to take the building apart in order to make sure that nothing continues to burn.

Firefighters are expected to remain at the scene for much of the night.

Everyone escaped: fire official

Fire spokesman Capt. Mike Strapko said it is believed everyone got out safely after the "six-alarm-plus" fire broke out inside the plant.

Before the roof collapsed, a partial structural collapse within the factory made it too dangerous to remain inside, so firefighters retreated and positioned themselves in a defensive attack around the exterior of the building, Strapko told CP24.

At the height of the fire, a huge cloud of smoke billowed into the sky and flames consumed several sections of the building.

A group of firefighters sprayed water on the blaze from the roof of a neighbouring building, while other teams used at least three ladder trucks to put out the flames.

The Office of the Fire Marshal was called in to investigate and the Ministry of Environment attended to conduct its own assessment of the situation.

Thursday’s fire is believed to be the first six-alarm blaze in Toronto since Jan. 3, 2011, when flames destroyed a heritage building at Yonge and Gould streets in the downtown core.

Investigators said the fire at Yonge and Gould was deliberately set.

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