NEW YORK

Before-and-after pictures show the unhealthy air conditions in New York caused by smoke from wildfires in Canada.

The images were compared with photos taken after the disaster.

On Thursday, June 8, the US National Weather Service has issued a warning that the unhealthy air conditions.

The current adverse weather conditions "will probably be hanging around at least for the next few days," said National Weather Service meteorologist Bryan Ramsey.

Smoke from hundreds of wildfires blanketed Canada.

Millions of Canadians have been told to stay indoors and forecasts for the most populated area in Toronto and region predict the smoke will increase through the end of the week.

As of Wednesday, 414 wildfires were burning, including 239 out of control. That's up from 211 wildfires reported at the end of May

Thousands of firefighters from around the world, including personnel from the US, Australia, New Zealand, Mexico and South Africa are battling the fires.

Wildfire season begins in early May as protective snow melts and lightning strikes and careless campfires ignite tinder-dry forests that cover much of the country.

Between March 1 and June 5, it is estimated that 2,214 fires have consumed 38,000 sq.km., making this year on track to be the worst in Canadian history.