An excavator ruptured a four-inch gas pipe this morning at the corner of Laurier Avenue and Le Jeune Street.
The excavator got stuck in the area where the pipe was ruptured, complicating efforts to cap the leak.
Gaz Metro is now working on ventilating the buildings affected by the leak.
The Montreal fire department, which evacuated a number of residences in the area, was called in shortly after 9.a.m. ET.
It has the final say on when residents can return to their homes.
Hydro-Québec says about 10,000 of its clients in the Plateau are also affected and have been without electricity for a few hours.