People across a wide area of the United States, including New York, were under alert on Wednesday due to poor air quality from thick smoke caused by wildfires in Canada.

New York Mayor Eric Adams warned that the city was experiencing an unprecedented level of air pollution, with residents observing dark orangish smoke and an unusual smell in the air. The conditions disrupted some flight schedules and led to the postponement of sporting events.

Smoky haze from wildfires in Canada diminishes the visibility of the Empire State Building on June 7, 2023 in New York City. (Getty/Kyodo)

"We're in the worst of the conditions" and the alert is expected to be in place until Thursday night, the mayor said in a Twitter post, advising people to wear masks and limit outdoor activities.

The same day, the city's air quality became the worst in the world due to the smoke, according to real-time rankings by Swedish air purifier maker IQAir AG.

The U.S. Federal Aviation Administration said it has slowed traffic to and from New York area airports due to reduced visibility from wildfire smoke.

The Canadian government said the country has had more than 400 wildfires as of Wednesday, with over 230 yet to be brought under control.

Major League Baseball said it postponed two games in New York and Philadelphia due to the poor air quality.