Four Republican members of Congress have accused Canada of failing to do enough to prevent wildfire smoke drifting into the US.

In a joint letter addressed to the Canadian prime minister, the Michigan lawmakers claimed “continued inaction” from Canada was “unacceptable”.

Canadian leader Mark Carney did not respond directly to the claims, but said that both countries had a responsibility to fight climate change.

As of Friday, there were more than 890 fires actively burning in Canada, according to the Canadian Wildland Fire Information System, external – with the majority burning out of control.

More than 190 of those are burning in Ontario, some out of control.

According to the Canadian Wildland Fire Information System, nearly 3 million hectares of land in Canada has already been destroyed by the wildfires.

The impacts have been far-reaching, with a thick blanket of smoke spreading across US states, from Minnesota and Michigan to Pennsylvania, Ohio and New York.

“Hazardous” air quality alerts have been issued across much of the region, leading to the cancellation of many outdoor events.

As of Friday, air quality in Detroit was worst in the world, Swiss air quality tracker IQAir said, external, followed by the Midwestern city of Chicago, Washington DC, and New York in seventh place.

In the open letter addressed to Canadian officials, US lawmakers John James, John Moolenaar, Jack Bergman and Lisa McClain said their “patience has run out”.

“We are done accepting apologies in place of action,” they said, warning the US could explore direct involvement in cross-border wildfire protection and firefighting if Canada failed to act.

“We were told last year that this would be treated with urgency. It was not,” they claimed, adding that instead “American lungs are paying the price for Canadian inaction, year after year”.

They said that issues such as “chronic under-investment in forest thinning, fuel reduction, and prescribed burns, along with inadequate enforcement against arson”, had not been addressed “adequately enough”.

But scientists BBC Verify have spoken to say the picture is more complicated.

“Weather doesn’t care about international borders,” says Dr Patrick James from the University of Toronto.

Once smoke reaches the atmosphere, it travels wherever the winds take it – and smoke from major US wildfires has also affected Canada in recent years.

Experts also say many of the current fires are burning in Canada’s vast, remote forests, where fires can be difficult to detect or contain before they become too large.

While better forest management can reduce wildfire risk in some areas, particularly near communities, it cannot prevent fires across an ecosystem of this scale.

Scientists also say increasingly severe wildfire seasons are being driven in part by climate change, which is creating hotter, drier conditions that allow fires to spread more easily.

“Climate change is a global issue, and it would be inaccurate to suggest that Canada alone caused or could have prevented these wildfires,” says Dr Anabela Bonada from the University of Waterloo.

Ontario Premier Doug Ford said on Friday that Canada has helped the US battle wildfires in California and respond to hurricanes in North Carolina.

“Maybe what you should do rather than complain is send support, send help, because we have done the exact same thing for our American friends,” Ford said.

Responding to the criticism from US lawmakers, Carney said in French during a news conference in Ontario: “Climate change is everyone’s responsibility – truly everyone’s – including the United States.”

He added that his government was “in close communication” with provinces and local communities.

Meanwhile, Ford dismissed criticism of his government’s handling of the fires, noting that over 150 fire crews are on the ground battling the blaze, along with over 80 water bombers and helicopters.

He added that his government has spent more than a billion dollars on wildland fire since 2018, and routinely spends more than the base budget allocated annually for firefighting based on need.

“We are throwing every single resource we can,” he said.

A large cluster of fires affecting northwestern areas of Ontario are responsible for sending thick plumes of smoke and poor air quality across the region.

On Thursday, thick haze of smoke blocked views across New York City, including the Empire State Building and the Statue of Liberty.

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

Namaygoosisagagun First Nation Chief Helen Paavola told local news outlet CityNews in an interview that an aerial flyover showed that her community has been “burnt to ashes”.

Ford said a total of 10 communities have had to evacuate, with many now seeking refuge in southern Ontario cities.

“It’s a miracle that no one lost their lives,” the premier said.

Roughly half of Canada’s wildfires are sparked by lightning, while the rest stem from human activity, data from the National Forestry Database shows. Expert have also warned that hotter temperatures are making the land drier and more prone to ignition.