Crews have begun to demolish what is left of a North York mansion gutted by an early morning fire on New Year's Day.

The multimillion-dollar house on Forest Heights Boulevard was under construction. The fire early Sunday left a burned facade.

Stephan Powell, District Chief for Toronto Fire Services, said Tuesday the building had to come down.

"The structure was unsafe," he said.

Powell said "it's far too early" to say what may have caused the fire, but arson has not been ruled out. 

"I don't think anything has been ruled out," Powell told CBC Toronto.

Large flames were visible going through the roof and the house's second-storey windows, and could be seen for some distance. The heat from the blaze was said to be intense.

North York mansion

Crews have begun to demolish a North York mansion gutted by a weekend fire. The mansion was under construction. (Christopher Langenzarde/CBC)

The Fire Marshal's Office is investigating the fire at the mansion near Bayview Avenue and Highway 401. Crews began demolition early Tuesday.

More than 80 firefighters were involved in fighting the blaze. It began at about 1:25 a.m. Sunday and was brought under control by 4 a.m.

Powell said he could not confirm whether investigators have spoken to the owners.

He said an estimate of the property damage is not yet available, but on the weekend he described the damage as severe.

The house was believed to be unoccupied at the time of the blaze, and no one was injured.

Toronto mansion under construction fire

It appears that only the shell of the mansion under construction remained after the New Year's Day fire. (Joe Fiorino/CBC)