DALLAS—Southwest Airlines said Sunday that hundreds of flights have been delayed by technical problems that are forcing it to check in some customers manually at airports and causing long lines.

In a statement, Southwest said it was still having "intermittent" technical issues on its website, mobile app and in its phone centers and airports check-in systems. It said that while it is working on the issues, workers at airports are helping customers with their itineraries.

Representatives for Southwest didn't say what caused the problem, or how much longer it was expected to last. The problems began Sunday morning and continued through the day, with 450 of the 3,600 flights set to operate affected by the delays.

The airline asked travelers to arrive at least two hours before their scheduled departures and to use airport kiosks to print boarding passes and tags for luggage.

At Los Angeles International Airport, dozens of people crowded the Southwest terminal, waiting to be issued handwritten tickets. The long lines at check-in meant some passengers didn't make their flights.

Emily Mitnick, who was flying to Detroit from Denver International Airport, said she missed her 10 a.m. flight, even though she parked her car around 8 a.m. She estimated that 1,000 people were in line at the check-in for a boarding pass. When she went downstairs to the curbside check-in, she said there were about a couple hundred people lined up there as well.

By the time she got to security, it was about 10:15 a.m.

"The clock was ticking and the flight took off," said Ms. Mitnick, who was trying to get to Detroit through a different flight to Chicago.

Last month, American Airlines experienced computer problems that prevented passengers from checking in and briefly halted flights on select routes. Airline officials said at the time that they fixed the problem after less than two hours, and that there was no indication that its system had been hacked.

Southwest is the top hauler of domestic passengers and the fourth-largest U.S. airline by traffic.

Copyright 2015 the Associated Press

(END) Dow Jones Newswires

October 11, 2015 20:55 ET (00:55 GMT)

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