OTTAWA, June 6 (Xinhua) -- 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.

Environment Canada issued special air quality statements for these areas on Friday, warning that people most likely to suffer health effects from air pollution should avoid strenuous activities outdoors and seek medical attention if experiencing symptoms.

Environment Canada's David Phillips said on CTV News that as wildfires ramp up across the country, air quality is deteriorating.

"What we've seen this week, of course, in Ontario is a lot of that smoke from fires has come south," Phillips said.

"Only a few see the flames but millions smell the smoke," he said.

According to data from Swiss air quality tracker IQAir, Toronto's air quality was ranked the second worst in the world Friday afternoon.