Air quality over New York and large parts of the north-eastern US deteriorated on Tuesday due to smoke spreading from wildfires in Canada's Quebec province.
The city topped a list of major cities around the world with the worst air quality, according to an online tracker called IQAir.
Its reading peaked at 196 on the index, an “unhealthy” level at least 28 times the guidelines set by the World Health Organisation, IQAir reported.
“Smoke from wildfires in Canada is impacting our city's air, so an air quality health advisory has been issued,” Mayor Eric Adams tweeted, advising people to take precautions if sensitive.
Detroit, in Michigan, was also ranked among the top 15 cities with the worst air quality on Tuesday.
Alerts were also issued in Connecticut, Massachusetts, New Hampshire, New Jersey, New York, Rhode Island and Vermont, AccuWeather reported, with radars showing smoke enveloping skies in the US north-east.
Toronto, Canada, which at one point reached the third spot globally, had a reading of 173 on the index.
There are at least 150 wildfires spreading in Quebec, according to the Canadian Interagency Forest Fire Centre.
“Year after year, with climate change, we’re seeing more and more intense wildfires – and they’re starting to happen in places where they don’t normally,” Canadian Prime Minister Trudeau said in a tweet.