Washington and Philadelphia have seen the worst air quality in years, as intense forest fires in Canada continue to affect millions of people. The poor environmental conditions have forced the cancellation of events and the suspension of flights across the United States.

Nearly 100 million people in North America are facing very poor air quality. US President Joe Biden described the fires as a "stark reminder of the impact of climate change".

Data from the US Environmental Protection Agency's Air Quality Index (AQI) show that North American cities had the worst air quality in the world on Thursday morning. Air quality in Washington, Philadelphia and New York was significantly worse than in cities in other countries, such as Lahore, Dhaka or Hanoi.

School trips and sporting events are being cancelled due to the smoke, and planned celebrations at the White House in the capital have also been called off. The National Zoo was also closed, and its animals, including three giant pandas, were moved indoors.
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