Fire crews are hoping to demolish an historic building in the heart of downtown Toronto that was destroyed by an intense blaze by late Tuesday afternoon.

But first, officials spent the day at the site battling hot spots and trying to find signs of what could have sparked the six-alarm fire.

Mike Ross, an investigator with the Fire Marshal's Office said he hasn't ruled out anything yet – including arson.

The building, located at Yonge and Gould Streets,  is believed to be about 100 years old and had been vacant since an exterior wall suddenly came crumbling down last April. The site was heavily boarded up so it appears unlikely that squatters could have been living on the property.

The property owner and local city councillor had been in talks about restoring the structure but yesterday Coun. Kristyn Wong Tam said she doesn't believe any amount of work could help save the building.

Ross told reporters at a news conference Tuesday morning that the front wall of the building (the one that faces Yonge St.) is very unstable.

"We can't have people driving by and have the wall fall down," he said.

Before crews begin to demolish the building later this afternoon, they must first dismantle the grates leading to the underground subway. They will have to be covered so debris doesn't fall through, Ross said.

Officials are monitoring the air for asbestos.

The aftermath of the fire is expected to continue disrupting traffic in the area. A stretch of Yonge Street remains closed north and south of Dundas Street for the investigation.

However, Ryerson University reopened today after it was forced to close its doors Monday.

At the height of the fire, 32 fire trucks and 125 firefighters were at the scene.