Firefighters got the call about the fire at 818 Godin Street near Bannantyne Avenue around 8:15 p.m. ET on Sunday, at which point the blaze was merely a two-alarm fire.
But it spread rapidly from the first floor to the attic in just 15 minutes, sounding all five alarms.
It took between 140 and 150 firefighters with 28 trucks more than two hours to get the fire under control, said Stéphane Corriveau, local chief of operations for the Montreal fire department.
The roof collapsed, making extinguishing the fire even more challenging.
The two buildings adjacent to the source of the fire were evacuated, and between one and two dozen people were put on buses to keep warm. No one was injured.
Authorities are looking to demolish the building under renovation.
The cause of the fire has not yet been determined.