Damaging storms swept through the Midwest, knocking out power to hundreds of thousands of customers and causing more than a thousand flight delays or cancellations at Chicago airports with more potentially severe weather expected Thursday.

The National Weather Service said it received more than a dozen reports of tornadoes Wednesday across northern Missouri, Iowa, Kansas and Illinois. There were no immediate reports of injuries or deaths.

Weather service meteorologist Frank Pereira said the frontal system that produced the storms, including high winds and hail, was moving eastward Thursday. There was also a slight risk of severe thunderstorms in parts of the Northeast and mid-Atlantic, where expected high heat and humidity spurred heat advisories by the weather service for Thursday and Friday.

The storms are being fueled by cool air from Canada clashing with warm, humid air from the South.

“Going forward, we’re expecting another area of severe weather to develop across portions of the central Plains, Midwest, particularly from Iowa, northern Missouri, northeastward through the Great Lakes,” Pereira said. “Again, it’s all tied into a pretty well-defined frontal system.”

Potentially dangerous heat and high humidity also was forecast Thursday and Friday for a swath of the East Coast from the mid-Atlantic to the Northeast, where daily high record temperatures could be broken in numerous places, the weather service said. Temperatures in the mid-90s Fahrenheit (mid-30s Celsius) were expected, but with the humidity it could feel like 100 degrees Fahrenheit (38 degrees Celsius) or more, the service said.

Philadelphia declared a heat health emergency for Thursday and Friday, activating cooling centers, home visits by field teams, outreach to people experiencing homelessness and other services. New York City officials were also urging residents to take precautions, including drinking plenty of water and finding a cool place to stay if they do not have air conditioning.

Wednesday storms moved into the Chicago area in the afternoon, downing trees and damaging some buildings.

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.

Air traffic appeared to return to normal Thursday morning, with only 24 flight cancellations and 34 delays nationwide, FlightAware reported.

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.

Around 390,000 customers had no electricity in the Midwest on Thursday. There were nearly 226,000 outages in Illinois, including around 150,000 in Cook County, while 85,000 homes and businesses were without power in Michigan, according to poweroutage.us.

Commonwealth Edison Company, which provides electric service across northern Illinois, said the storms had downed poles and wires.

“We know this is challenging and will restore service as safely and quickly as conditions allow,” the company said in a post on X.

The storms soaked Rate Field in Chicago before Wednesday night’s game between the White Sox and the Atlanta Braves.

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The story has been updated to correct the name of the White Sox stadium to Rate Field, from Guaranteed Rate Field.

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Associated Press reporter Dave Collins contributed from Hartford, Connecticut.