Toronto, New York and Washington top list of most polluted cities

Cities across north-eastern Canada and the US are continuing to suffer from intense smoke brought on by hundreds of wildfires burning across Canada.

On Saturday, Toronto, New York and Washington DC recorded some of the worst air quality levels in the world, prompting health warnings from local authorities urging people to limit time outdoors because of the risks posed by the smoke.

Many of the wildfires remain out of control, forcing evacuations and destroying homes and infrastructure. The blazes left one tribal community completely decimated in northern Ontario, ripping through the Namaygoosisagagun First Nation with little warning.

Canadian officials said on Saturday that fire activity in Ontario was beginning to ease, with air quality expected to improve in US cities later in the day.

The smoke has also fuelled political tensions across the border. US President Donald Trump has threatened to impose new tariffs on Canada to offset what he described as the "incalculable" cost of the smoke's impact on his country.

Poor air quality in the New York region is also prompting concerns for Sunday's World Cup Final in New Jersey.