(CNN) -- Air traffic controllers worked to clear a backlog of delayed flights at Chicago's two major airports Tuesday after smoke at a radar facility prompted a ground stop.
The smoke was caused by a faulty motor in the HVAC system, according to a statement from the Federal Aviation Administration. There was no fire.
"Air traffic controllers returned to work in the Chicago Terminal Radar Approach Control (TRACON) facility in Elgin after FAA technicians cleared the residual smoke from the radar room," the agency said in a statement.
Earlier, FAA personnel were evacuated from the facility.
Airlines at both O'Hare International and Chicago Midway were reporting significant delays and cancellations Tuesday afternoon, according to a statement from the Chicago Department of Aviation.
At O'Hare, most flights in and out of the airport were delayed by an average of an hour or more, and more than 600 flights had been canceled, the department said. Some 75 flights were canceled at Midway.
TRACON air traffic controllers take control of long distance flights as they approach. They then guide traffic to just a few miles from the airport, before handing off to a controller who handles landings on a runway.
CNN's Mike Ahlers and Thom Patterson contributed to this report.