CHICAGO, Illinois (CNN) -- Hundreds of passengers lined up Thursday outside the United Airlines terminal at O'Hare International Airport after a computer outage delayed incoming and outgoing flights, the airline and witnesses said.
United Airlines passengers wait in line Thursday at O'Hare International Airport in Chicago.
The problem could result in flight cancellations, said Karen Pride, spokeswoman for the Chicago Department of Aviation.
She said she could not confirm how many passengers were affected or how severe the delays were.
CNN Chicago affiliate WGN-TV estimated about 2,000 people were in a line that began inside the terminal and stretched outside.
"While we immediately work to fix it, flights are delayed and some may be canceled," the airline said in a statement. "We apologize to our customers for this inconvenience and recommend they allow for extra time at the airport and use united.com to check flight status and check-in."
United had no estimate of when the problem would be repaired at O'Hare.
CNN's Kara Devlin contributed to this report.