Stop lights went out on many streets, including at Sherbrooke Street and Décarie Boulevard, while power to the lights in the Décarie Expressway tunnel was also cut.
The electricity in many of those areas was restored by 6 p.m.
The gas leak happened on Marcil Avenue at about 3 p.m. when a gas line was cut during a sidewalk excavation.
About 30 firefighters were at the scene and set up a security perimeter on Marcil between Monkland Avenue and Somerled Avenue in N.D.G. A dozen homes had to be evacuated.