MONTREAL -- A major power outage in Montreal left 65,740 caused service interuptions for 65,740 people mainly in the Notre-Dame-de-Graces, Hampstead, Cote-des-Neiges and Cote-Saint-Luc regions.

By 12:30 p.m., power returned for most customers.

"It came from the Hampstead substation. We don't know the exact cause, but we're investigating," said Hyrdo Quebec spokesperson Catherine Savoie shortly after the outage.

This is a developing story that will be updated.