Smoke from more than 100 wildfires blazing in Canada is expected to spread to impact air quality in more U.S. state.

Smoke from Canadian wildfires worsened air quality in the eastern U.S. on Wednesday as several Midwestern states battled conditions deemed unhealthy by the federal government. The fires have forced thousands of Canadians to flee their homes and sent smoke as far as Europe.

Wildfires burning in western Canada have produced smoke that, carried by steering winds, has reached the eastern U.S., raising growing concerns about poor air quality.