The Federal Aviation Administration said no planes in the United States destined to cross the Midwest would be allowed to depart until at least 10 a.m.
As of 8:30 a.m., 435 flights had been canceled at O'Hare and 395 delayed, according to FlightStats, which collects data from airports and airlines. At Midway, nearly 100 flights have been canceled and nearly 40 delayed.
Southwest Airlines told passengers at Midway that all of its flights there have been canceled until noon.
Emergency crews were called to a fire in the facility's basement around 5:40 a.m., according to Aurora Police Sgt. Dan Ferrelli, a department spokesman. They found a man there with "self-inflicted non-gunshot" wounds and transported him to a hospital, Ferrelli said.
He said 15 to 30 employees at the center were evacuated. One employee, a man about 50 years old, was treated at the scene for smoke inhalation.
The fire has been extinguished and the investigation was continuing, Ferrelli said. He would not say if police suspect the fire was set.
The Aurora radar facility, called Chicago Center, is an en route air-traffic facility that handles high-altitude traffic across parts of the Midwest.
Controllers at the center direct planes through the airspace and either hand off the air traffic to other similar facilities handling high-altitude traffic in the U.S., or direct the planes to terminal radar facilities, including one in Elgin, which in turn direct planes to and from airport towers.
It was unclear how long the ground stop at O'Hare and Midway would last. The FAA website said planes departing from anywhere in the U.S. that are destined to travel through the Aurora facility will not be allowed to depart until at or after 10 a.m., Chicago time.
Flights already in the air have been handed off to other air traffic control centers. "Airspace management has been transferred to adjacent air traffic facilities," said FAA spokeswoman Elizabeth Cory.
Cassandra Dump, a 30-year-old publicist, was headed for a Central Park concert in New York featuring Jay Z, Sting and No Doubt when she got stranded at Midway.
She boarded the first plane she could get, only to be told by the flight crew that all planes had been grounded.
"Fifteen minutes later, they let us know we could get off the plane if we wanted. You could take your ID with you, grab coffee but stay near the gate area," she said. "Then about 10 minutes later, by 6:30, 6:45, we're completely off the plane, deplaned, because they didn't know what happened to the flight."
She paused while a message played over the airport PA system saying all planes out of the Southwest terminal had been canceled until at least noon.
She said there weren't too many irate people. "No one's too pissed, everyone's been up since 3 a.m. I think everyone's just tired."
Hundreds of people were in the terminal near her, she said, everyone waiting on announcements from the airlines.
Some websites haven't been able to keep up and still listed some flights as on time, she said.
Her plan was to find another way to New York. "I'm going to go online and see if I can re-book," she said. "I'm not going to miss (the concert). I'll walk to New York."