Thousands of flights have been delayed and baseball games postponed across the US east coast as smoke from Canadian wildfires continues to drift south, covering cities in a yellowy-brown haze.

Canadian officials say this is shaping up to be the nation’s worst wildfire season ever.

Forest fires have scorched 9.4 million acres of the country and forced 120,000 people from their homes.

The country’s wildfire season has begun early on ground that is drier than normal and accelerated quickly – with smoke from the wildfires pouring into the US east coast and mid-west.

The US National Weather Service has issued air quality alerts for almost the entire Atlantic seaboard.

Health officials from Vermont down to South Carolina, and as far west as Ohio and Kansas, have warned residents that spending time outdoors could cause breathing problems.

In Manhattan, a Home Depot store sold out of air purifiers and masks, while the number of face coverings in use recalled the height of the COVID pandemic.

New York’s famous skyline has lost its sharp edges, the air smelling like burning wood.

In some areas, the air quality index, which measures major pollutants produced by fires, was well above 400, according to Airnow, which describes 100 as “unhealthy” and 300 as “hazardous”.

With weather systems expected to remain broadly static, the smoke, billowing down from Quebec and Nova Scotia, could persist into the weekend.

US National Weather Service meteorologist Bryan Ramsey said it will “probably be hanging around at least for the next few days”.

He added: “Since the fires are raging – they’re really large – they’re probably going to continue for weeks. But it’s really just going to be all about the wind shift.”

British actress Jodie Comer was forced to stop a matinee performance on Broadway after she began coughing on stage only 10 minutes into her performance.

In baseball, the New York Yankees and the Philadelphia Phillies both postponed home games scheduled for Wednesday.

A National Women’s Soccer League match in Harrison, New Jersey, was also rescheduled, as was a WNBA women’s basketball game in Brooklyn.

It is not the time to “train for a marathon or do an outside event with your children”, advised New York Mayor Eric Adams.

“If you are older or have heart or breathing problems, you should remain inside.”

New York Governor Kathy Hochul said the state was making a million N95 masks available at state facilities, including 400,000 in New York City.

In Washington DC, Mayor Muriel Bowser ordered schools to cancel outdoor breaks, sports and field trips on Thursday.

In suburban Philadelphia, officials set up an emergency shelter so people living outside can take refuge from the haze.

Back in Manhattan, Tyrone Sylvester, 66, was playing chess in Manhattan’s Union Square as he has on most days for the last 30 years.

He was wearing a mask. “When the sun looks like that,” he said, pointing at its dulled outline through the smoky sky, “we know something’s wrong”.