In pictures: Smoke from wildfires turns North American skies orange

Tens of millions of people in North America are being urged to wear face masks outdoors after large areas of the US and Canada were blanketed by thick smoke from wildfires.

Traffic goes over the Ed Koch Queensboro Bridge in New York City as smoke from Canadian wildfires casts a haze over the area

There are dozens of wildfires currently burning across Canada, but the prevailing wind has pushed smoke from several large ones in Ontario and Quebec south across the border with the US.

A person wearing a face mask waits for the subway in New York City with an orange, smokey sky in the background

The smog engulfed the CN Tower in Toronto (below left) as it passed through the city earlier this week, before shrouding the Statue of Liberty in New York (below right).

Smoke from forest fires creates a pink hazy sunset over Toronto The Statue of Liberty surrounded by heavy smog in New York
A person wearing a mask and riding scooter passes as buildings in lower Manhattan are seen through smoke filling the air Members of the US Marine Corps rehearse in hazy smoke at the Lincoln Memorial in Washington DC

The advice to residents in New York, Philadelphia and Washington DC is to stay inside when possible - but that didn't put these people off taking a fitness class on top of a Manhattan skyscraper.

People attend a morning yoga class on top of a building in Manhattan, New York People attend a morning yoga class on top of a building in Manhattan, New York

The air quality is so bad in New York that officials are distributing one million masks to residents, with the conditions expected to persist into the weekend.

A person walks dogs along the Brooklyn promenade as the Manhattan skyline is shrouded in haze
A traffic officer wears an N95 mask in Times Square amid a smoky haze from wildfires in Canada People take photos of the Manhattan skyline during heavy smog in New York People play basketball in Brooklyn Bridge Park as the Lower Manhattan skyline is obscured by hazy skies A person on the subway wears a face mask as smoky haze from wildfires in Canada blankets a neighborhood

Firefighters in Canada are still tackling more than 400 blazes across the country, with over 200 of them considered out of control. Thousands of people have been forced to evacuate affected areas.

Firefighters at one of scores of wildfires burning in Edson, Alberta Smoke billows from the West Kiskatinaw River wildfire and Peavine Creek wildfires in the Dawson Creek Zone, British Columbia A Canadian firefighter at a wildfire in Sturgeon Lake Cree Nation