Image caption, Smoke from the wildfires is causing poor air quality across New York City, with hazy skies captured on Wednesday ByChris Fawkes, BBC Weather and Rachel Flynn Published 4 minutes ago More than 800 wildfires are burning across Canada, with air quality alerts now extending south into multiple US states.
The air quality in large parts of the northern states of Michigan, Minneapolis and Minnesota is deemed "hazardous" by the US Air Quality Index program, with people recommended to stay indoors.
Alerts span the Upper Midwest, the Great Lakes region and into the US's Northeast, the US's national weather service (NOAA) said in an update on Thursday.
There are currently 857 fires actively burning in Canada, including 23 new fires on Thursday, according to the Canadian Interagency Forest Fire Centre.
Figure caption, Watch: Orange haze from Canada wildfires seen in Ontario and northern US According to the Canadian Wildland Fire Information System, the vast majority of wildfires are burning out of control.
The large cluster of fires affecting western areas of Ontario are responsible for sending thick plumes of smoke and poor air quality across Thunder Bay and Toronto, with lower concentrations of smoke high in the atmosphere drifting over the Great Lakes and above New York with hazy skies and redder sunrise and sunsets likely.
There will be quite widespread thunderstorms in Ontario over the next few days, but the rain may not be enough to make much of a difference.
Northwesterly winds will continue to blow the smoke into northern US states for the rest of this week and into the weekend, leading to concerns smoke will drift into New Jersey where Sunday's World Cup final is due to take place.
A change in the wind direction by Monday means that the smoke will tend to be steered across Quebec with an improvement in air quality further south in the US.
Air quality in the Midwestern city of Detroit is currently the worst in the world, Swiss air quality tracker IQAir said, followed by Minneapolis and Toronto.
Figure caption, Dramatic video shows wildfire surround freight train in Canada A dramatic video on Wednesday showed a freight train in Ontario, Canada surrounded by wildfire flames, as workers requested an emergency rescue.
Canadian National Rail said in a statement that the workers who were trapped outside Armstrong were all safely rescued, and that operations have been temporarily suspended in the region.
