The fire broke out around 11 a.m. in the basement of Prestige DB, a formal wear store in the St-Hubert plaza. That building, as well as the buildings on either side, have been evacuated.
One plaza employee was rushed to hospital.
Several businesses in the area have had their electricity turned off and are closed.
St-Hubert Street is closed to traffic between Beaubien Street and St-Zotique Street.
The cause of the fire is still unknown, but earlier this morning, there were attempts to thaw frozen pipes in that building. No connection has been established yet.