According to the utility, two protective devices tripped on two transmission lines originating in James Bay and arriving in southern Quebec around 3 p.m. Thursday,
Most of the power failures were on the island of Montreal, but areas in Laval and the Laurentians were also affected.
Hydro-Québec is asking customers in Montreal, Laval, the Laurentians, the Outaouais region and the Eastern Townships to curb their consumption between 6 a.m. and 9 a.m. this morning.
Customers can help by turning down the temperature in unoccupied rooms and by postponing the use of major appliances like dryers and dishwashers by a few hours.
The utility said workers began inspecting the lines last night but that it was difficult to perform their functions in the dark.
They will resume their work at daybreak this morning.