Several Midwestern U.S. states have issued air quality alerts to residents as smoke from Canadian wildfires begins to move south.

Mandatory evacuation orders have been issued for communities in remote northern Alberta as the province braces for another day of potentially explosive wildfire activity.

Canada, the world’s fourth-largest crude producer, has long seen its energy output threatened by wildfires that rage through the dense forests of northern Alberta in spring and summer. In 2016, a blaze shut down the massive oilsands mines just north of Fort McMurray, taking more than one million barrels of daily production offline.

Alberta isn’t the only province grappling with fires. Manitoba declared a province-wide state of emergency on Wednesday amid intensifying blazes in the northern part of the province, with the largest evacuation centered on Flin Flon, Man. where at least 17,000 people have fled the blazes.

Ferocious wildfires in western Canada have forced thousands of people to flee their homes in Manitoba. Some 17,000 Canadians were evacuated before the blaze spread to neighbouring Saskatchewan. Scott Moe,

Hot air rises very quickly, which means that the smoke and ash from these fires can reach high heights in the atmosphere. The upper level winds then take that smoke, and they blow it hundreds of miles away. That's why many North Carolinians are seeing a hazy sky over the state Saturday.

The Canadian province of Manitoba has declared a state of emergency over a series of wildfires, and Prime Minister Mark Carney has agreed to send in the military to help.