Millions of Americans face air quality alerts from Minnesota to New York as authorities urge people to stay indoors

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Smoke from wildfires burning in south-central Canada and parts of Minnesota is spreading across the US, prompting air quality alerts in more than 20 states with millions of Americans expected to face unhealthy air conditions this week.

The smoke from the more than 180 active wildfires in northern Ontario briefly made Toronto’s air quality among the worst in the world on Wednesday. By Wednesday night, the smoke had spread across several US states, from Minnesota, where multiple wildfires are also burning, to New York, blanketing the skies in haze and worsening air quality.