Determining a cause will be the next step following a six-alarm, pre-dawn downtown fire that destroyed a boarded-up heritage building and left four firefighters with minor injuries.

One avenue of investigation will be whether someone deliberately set the fire.

"The power, gas, hydro, water -- everything was shut down," Coun. Kristyn Wong-Tam (Ward 27, Toronto Centre-Rosedale) told reporters from the scene at Gould and Yonge Streets, just north of the Eaton Centre.

A security fence has surrounded 335 Yonge Street since April, when a portion of the brick wall crumbled down. That made it unlikely squatters had entered the structure, she said.
Mike Ross of the Ontario Fire Marshal's Office said they will look at all possible causes, including arson.

"We haven't confirmed anything. We haven't eliminated anything. But that will be a consideration," he said.

Investigators will have to sort through about 3 metres of debris to determine a cause, but Ross said they believe the fire started on either the second or third floor.
However it started, the fire put two firefighters into serious danger.
The rescue
The firefighters slipped from an icy rooftop following a gust of wind and fell about six metres into the fire shortly after 5 a.m. as more than 125 crew members fought to contain the blaze.
"You're free-falling. You can't see anything. So I imagine that it's pretty scary," Fire Chief William Stewart told reporters, adding "the heart dropped right out of my chest."
He said a rapid extraction team managed pulled the two men from the fire after a tense 24-minute rescue mission.
They were removed just before the walls crumbled.
"It's a very horrific situation for the firefighters on the scene," Stewart told reporters. "You have to locate them in the smoke, find out where they are and extricate them from the building. The training that we put our people through worked most effectively. You can tell by the smiles on the faces this morning that it was a good rescue."
CTV Toronto's Austin Delaney, reporting from the scene, said firefighters lowered a U-shaped firehose into the hole, then pulled the trapped firefighters to safety.
A parallel effort tried to punch a hole into the building from the adjacent HMV store as water was sprayed on the trapped men.
The two men and another firefighter were taken to St. Michael's Hospital but released with minor injuries later that morning.
One of the men suffered injuries to his lower back, but Stewart said he would recover. "He'll certainly be sore," he said.
A fourth firefighter injured his hand in the rescue but refused to be taken to the hospital, instead staying to fight the blaze.
The damage
The fire broke out shortly after 4 a.m. just north of Yonge and Dundas Streets, one of Toronto's busiest downtown intersections.
Yonge Street was closed in the fire area, leaving access to local businesses restricted, with some suffering water damage. Ryerson University's nearby campus was also closed for the day.
As many as 32 trucks were called to the scene, including five aerial towers that were used to shoot water down on the blaze.
Toronto Fire Services Captain Mike Strapko said they were hesitant to send firefighters into the building because it has a history of being unsound.
In April, the downtown area was evacuated after a brick wall collapsed from the exterior of the same building. The century-old building had been declared a heritage site.
The building sat empty since the wall collapse. It was most recently home to the Salad King Thai restaurant.
Wong-Tam said she had tried several times to contact the building's owners and proceed with renovations.
The building, built in 1893, was once home to the Empress Hotel. Wong-Tam said she had scheduled a meeting with structural engineers for January 10 to discuss a renovation schedule.
Ken Rutherford of the Yonge Street Business Improvement Association said it's important to all area businesses to repair such buildings as quickly as possible.
CTV Toronto attempted to contact the building's Mumbai-based owner for comment, but was unsuccessful.
Local businessman Raza Khan said his business was destroyed in the fire. "It's a huge shock. It's a disaster," he said.
Khan and other tenants haven't been allowed in the building since the wall collapse.
HMV representatives told CTV they are concerned about heavy water and smoke damage from the next-door fire.
Officials say businesses should be able to open as usual on the west side of Yonge Street on Tuesday. But businesses on the east side near the fire site might still be closed.
Ryerson plans to resume classes Tuesday.
With reports from CTV Toronto's Austin Delaney and Zuraidah Alman