More than 800 wildfires are currently burning across Canada, sending smoke southwards and triggering air quality alerts across large parts of the northern United States. The blazes, most of which are out of control, have made air quality "hazardous" in states including Michigan and Minnesota, with residents advised to stay indoors, while Detroit was ranked the world's worst city for air pollution by tracker IQAir.

Canada's Interagency Forest Fire Centre recorded 857 active fires, including 23 new ones on Thursday, with a large cluster in western Ontario sending thick smoke over Thunder Bay and Toronto and hazier skies as far as New York. Northwesterly winds are expected to keep pushing smoke into the US through the weekend, raising concerns it could reach New Jersey ahead of Sunday's World Cup final, though a shift in wind direction from Monday should steer smoke towards Quebec and ease conditions further south. Separately, a freight train crew near Armstrong, Ontario, had to be rescued after becoming surrounded by fire, according to Canadian National Rail.