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 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 northeast, the US 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.

According to the Canadian Wildland Fire Information System, the vast majority of wildfires are burning out of control.

The large cluster of fires affecting northwestern 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.

Republican lawmakers in the state of Michigan have penned an open letter to Canadian Prime Minister Mark Carney asking for better management of the country's wildfires, expressing frustration for the third year in a row.

"A year has passed, the season has come around again, and nothing has changed except that our patience has run out," said the letter, signed by four House representatives from the US state.

Pete Hoekstra, the US ambassador to Canada, struck a more diplomatic tone in a statement on Wednesday commending wildfire fighting efforts from both countries.

"This challenge knows no borders. The United States will continue to coordinate closely with Canada, just as we have for more than four decades of shared wildfire emergencies," he said.

In addition to the hazardous smoke, the wildfires in northern Ontario have forced hundreds from local First Nations communities to evacuate, with videos showing some fleeing the remote area by boat.

Homes and buildings in the area have also been damaged extensively by the flames, said Anishinabek Nation Grand Council Chief Linda Debassige in a statement.

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.