Fifty people have been left homeless after the massive fire broke out late Friday afternoon in the basement of 1070 Mackay Street, just south of René-Lévesque Boulevard.
More than 150 firefighters were called to the scene to control the fire, which did not damage the neighbouring buildings.
The fire was initially treated as accidental, but was later transferred to the police arson unit.
“It’s impossible to establish the exact causes of this fire so this is the reason why our investigators will go on the scene this morning,” said Constable Simon Delorme with the Montreal police.
The building was a former hotel, which was renovated several times before finally being converted into social housing.
Nobody was injured in the fire, but the Red Cross was called to help victims.
The building had to be completely demolished following the fire.