(Bloomberg) -- Efforts to restore power to hundreds of thousands of people in Ontario and Quebec are set to continue for days after thunderstorms Saturday caused severe damage, leaving at least 10 people dead.  

Hydro Quebec and Hydro One have a combined 367,250 clients still affected by outages, according to their websites at 4:38 p.m. Toronto time on Monday. Hydro Ottawa, which serves the nation’s capital, has about 143,000 customers without electricity. Alectra Utilities, which operates in suburbs and outlying regions around Toronto, is also still trying to restore full service.  

A weather phenomenon known as derecho, made of long-lasting windstorms associated with a line of thunderstorms, developed near the Canadian border city of Sarnia, Ontario, and tracked over southern parts of the province on Saturday morning. The severe weather hit Toronto before heading toward Ottawa and parts of Quebec. 

At least 10 people died as a result of the strong winds, which were measured at 132 kilometers per hour (82 mph) in a location west of Toronto, according to the national weather service. At one point, more than 1 million people were without power. 

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