Damaging storms swept through the Midwest on Wednesday, knocking out power to hundreds of thousands of customers and causing more than a thousand flight delays or cancellations at Chicago airports.

The National Weather Service issued tornado warnings across Illinois, Kansas, northern Missouri and southern Iowa, while severe thunderstorm watches were in place for parts of the Great Lakes.

The Chicago area was in store for a one-two punch of weather. Storms that moved in Wednesday afternoon, downing trees and damaging some buildings, were expected to be followed by more wild weather in the evening. The National Weather Service warned of storms moving eastward across northern Illinois and potentially bringing “damaging winds, a brief tornado or two, and localized torrential rainfall increasing the risk for flash flooding.”

The two major Chicago airports, Chicago O’Hare International Airport and Chicago Midway International Airport, temporarily put all flights on hold in the evening due to thunderstorms. A similar ground stop was issued at John F. Kennedy International Airport in New York due to thunderstorms.

By Wednesday evening, more than 1,000 flights going into and out of Chicago had been delayed or canceled, according to FlightAware, a flight tracking website.

Strong winds blew part of the roof off an apartment building in the Chicago area, forcing residents to leave, according to NBC 5 Chicago. Elsewhere, barns collapsed in Wisconsin, buildings were crushed in rural northern Missouri and some large trees and power lines were downed in other areas across the Midwest, photos and video online showed.