Canada wildfires: Smoke choking major US cities

Smoke from hundreds of wildfires burning in Canada has prompted air quality warnings across parts of the United States on Friday, triggering fresh tariff threats from US President Donald Trump.

More than 800 wildfires are burning across Canada and the clouds of dense smoke have spread south, choking major cities including Detroit, Chicago, and New York.

Both Detroit and Chicago issued air quality index readings in the "hazardous" range, while in New York, the metro area was shrouded in a smoke tinted haze, deemed unhealthy for sensitive groups. 

National Weather Service (NWS) forecasts have warned that conditions may worsen overnight into Saturday morning.

The AFP news agency cited NWS meteorologist Peter Mullinax as saying that wind over the Great Lakes region could cause more smoke to pour into the Northeast, which could keep skies hazy.

There is concern from some air quality forecasters that more smoke is blown south after weekend weather systems.