Smoke from wildfires is expected to cause poor air quality and reduced visibility, according to an alert issued by Environment Canada on Thursday.

Smoke from wildfires burning in northern Ontario and the Prairies of Canada caused poor air quality and reduced visibility in major cities including Toronto, Ottawa and Montreal on Friday.

Smoke from Canadian wildfires carried another day of poor air quality south of the border to the American Midwest. Huge plumes of smoke have even reached Europe, the European Union's climate monitoring service said Tuesday.