The U.S. on Friday said Holtec's planned restart of the Palisades nuclear power plant in Michigan would not harm the environment, a needed step in its plan to become the first such plant to return from permanent shutdown.

"This is the largest evacuation Manitoba will have seen in most people's living memory," Manitoba Premier Wab Kinew said in a news conference on Wednesday.

Thousands of people fled from areas overwhelmed by wildfires in Canada's northern Manitoba. The outbreak of fires across much of western Canada's north is due to unusually hot and dry conditions and flames are consuming hundreds of thousands of hectares of tinder-dry forest and bushland.

Smoke from wildfires in Canada has begun drifting across the border into the United States, raising concerns on Friday about possible health hazards in the Upper Midwest, the authorities said.