Air quality plummets as Canadian wildfire smoke stretches across the Midwest

Haze from Canadian wildfires blankets the Chicago skyline as seen from the city's South Loop neighborhood on Wednesday. (Kathleen Foody/AP)

Smoke from wildfires in Canada is again blanketing parts of the U.S. with a thick haze that's reducing visibility and prompting air quality warnings in several states.

States across the Midwest are bearing the brunt of the wildfire smoke, which for a short time on Tuesday caused Chicago to have among the worst air quality in the world.