Traveling smoke from the Canadian wildfires contain pollutants such as carbon monoxide and nitrogen dioxide, two of the five toxins the US Environmental Protection Agency uses to determine an area's Air Quality Index (AQI).

AQI indicates how clean or polluted the air is around you. The index runs from 0-500 and the higher the number, the worse it is for your health.

Anything from 151-200 is designated as "unhealthy". When the number is between 201-300 it's "very unhealthy" and the the risk is increased for everyone. The highest level is "hazardous" and occurs when the AQI is above 301.

Here are some of the current US AQI values most impacted by the wildfires in Canada:

• Ottawa, Ontario, Canada - 235
• Toronto, Canada - 158
• New York, New York - 168
• Montreal, Quebec, Canada - 34

We have a camera over the city skyline, showing how bad the smoke really is.

You can watch the live stream by clicking the Play button at the top of the page.

Image source, Getty Images

In Toronto and much of the Canadian province of Ontario, the air quality index is projected to be at "high risk" levels until at least Thursday evening.

Environment Canada predicts poor air quality will likely persist into the weekend.

The New York State Air Quality Index also projects air levels to remain "unhealthy" for New York City and Long Island on Thursday.

Washington DC is also bracing for poor air levels into Thursday as smoke drifts south.

A storm system off the coast of Nova Scotia is the driving factor behind the wildfire smoke traveling south into the US and then towards the east.

Environment Canada says a low pressure system may bring cleaner air to the region on Sunday.

It is expected that the smoke will still be seen and felt for the next few days, as fires in Quebec continue to burn.

As of Wednesday, the Canadian province has 149 active forest fires, with most of them deemed out of control.

Image source, Getty Images

Hazy and polluted skies overhead this week are an unusual sight for most Americans, but in other parts of the world, they can be fairly common.

Major cities in parts of Asia, Africa and Latin America often see dangerous air quality levels like the ones seen in New York today.

South Asia is particularly polluted, with a World Health Organization report , externalfinding the region suffers an estimated 2 million premature deaths per year due to air pollution.

The worst is Delhi, the capital city of India. It places first on IQAir's rankings for air quality in major metro areas around the world, with an "unhealthy" Air Quality Index (AQI) score of 191.

Several other Asian cities make IQAir's top 10: Hanoi, Vietnam; Dhaka, Bangladesh; Jakarta, Indonesia; and, Shanghai, China.

Several more Chinese cities feature further down the list.

New York City is currently sitting on an AQI of 171, but reached as high as 200 overnight.

At a press conference just now, New York City Mayor Eric Adams urged residents to protect themselves from the poor air quality.

"Yesterday, New Yorkers saw and smelled something that has never impacted us on this scale before," he said.

"This is an unprecedented event in our city and New Yorkers must take precaution."

The city has issued air quality health advisory in each of its five boroughs, and public schools have cancelled outdoor activity, with conditions expected to worsen into Thursday.

"We recommend vulnerable New Yorkers stay inside and all New Yorkers should limit outdoor activity to the greatest extent possible," said Mayor Adams.

"Close windows and doors and use air purifiers if you have them," he added. "If you're an older adult or have heart or breathing problems, you should remain inside. If you must go outdoors, wear high quality masks, such as an N95."

The New York Yankees are as iconic to the city as the Empire State Building and the Statue of Liberty.

And these hazy weather conditions made for incredibly striking images at last night's baseball game.

Check out these pics:

Image source, Getty Images

Image source, Getty Images

Nadine Yousif
Reporting from Toronto, Canada

Image source, Getty Images

Officials tend to issue warnings when wildfire smoke levels in the air are this high - and for good reason.

Exposure to wildfire smoke can cause a litany of health issues, says Matthew Adams, the director of the Centre of Urban Environments at the University of Toronto.

Immediate effects include shortness of breath, an elevated pulse, chest pain, or inflammation in the eyes, nose and throat.

"On these elevated air pollution days, we'll see an increased number of visits to hospital," Adams says.

Adams cautions that there are also longer-term effects of wildfires, especially for people who are frequently exposed to smoke.

Those include higher rates of cancer and lung disease. Studies have shown that wildfire smoke can also impact pregnant women and their unborn babies, Adams says.

His advice to people is to limit time outside as much as possible to avoid breathing in the smoke.

Officials have said that Canada is shaping up for its worst wildfire season on record.

There are more than 150 active wildfires burning across Quebec.

More than 400 wildfires have ignited in the province so far in 2023, twice the average for this time of year.

Fires across Canada have already burned more than 3.3m hectares of land - an area 12 times the 10-year average for this time of year.

As well as Quebec, major fires have also been burning in British Columbia, Alberta, Ontario, Nova Scotia and the Northwest Territories.

Thousands of people have been evacuated across the country.

Outdoor activities at public schools in New York and Washington DC have been suspended.

New York's Department of Education announced the news last night, as Mayor Eric Adams warned that conditions in the city would likely get worse.

"Where possible, activities can be moved inside," the agency said on Twitter.

It added that schools remain open but: "We urge everyone to reduce prolonged or heavy exertion outdoors".

In America's capital city, the school system made its decision as the local government declared a "Code RED" air quality alert on Wednesday morning.

The alert means that "air pollution concentrations within the region are unhealthy for everyone with special precaution for sensitive groups such as children and those suffering from asthma".

School children were urged to avoid strenuous activity and exercise outdoors, including recess, physical education classes and athletic practice sessions.

Tens of millions of people in North America have been warned about potentially dangerous air quality as intense wildfires burn across Canada.

Smoke blanketed large areas of Ontario and Quebec, while an orange haze hangs over much of the north-eastern US.

Some cities including Toronto and New York briefly had the worst air quality in the world overnight.

Environment Canada issued its strongest air quality warning for Ottawa on Tuesday, deeming it a "very high risk" to people's health.

In Toronto and its surrounding areas, the air quality was classified as "high risk".

Meanwhile, the US Environmental Protection Agency (EPA) classified the air quality in much of the north-east as "unhealthy" especially for people who already have respiratory issues.

In total, some 100m people around North America are thought to be under a form of air quality warning.

You can read more about the situation here.

Brandon Livesay
Live reporter

Image source, Getty Images

Hello and welcome to our live coverage of the Canada wildfires, which has caused dangerous air quality in some of North America’s largest cities.

Like millions of New Yorkers, I woke up today to an eerie orange glow as the sun tried to break through the thick haze blanketing the city.

People are wearing masks outdoors to protect themselves from what was among the worst air quality levels in the world.

You can feel it sting your eyes and hit the back of your throat while walking outdoors.

And the situation is worse in Canada, where the country is dealing with what looks to be its worst wildfire season on record.

Some 160 fires are burning in Quebec. Across the country more than 3.3m hectares of land has burned already.

Stay with us as we bring you the latest updates.