Southwest Airlines grounded its aircraft for several hours after an internal computer system used to dispatch flights went down Friday night, an airline spokeswoman said.
Any flights that were in the air when the glitch occurred at about 11 p.m. ET were OK and could land, but any flight that hadn't departed was grounded, said spokeswoman Michelle Agnew.
A little after 2 a.m. ET Saturday, the airline tweeted that the problem had been fixed and flights would begin departing.
In a statement, Southwest Airlines said it was not known what caused the outage.
“It's looking like ultimately about 250 flights, mainly out West given the time of day, were impacted - that's out of about 3,400 flights scheduled today [Friday],” the statement said.
"We sincerely appreciate everyone's patience as we work diligently now to get people where they are supposed to be. Because it is late and this is a slow ramp-up back to normalcy, there still could be some cancellations - but we're working hard to get everyone in the air."
The Associated Press reported later Saturday that Southwest had canceled at least 64 flights due to the glitch, but that the computer system was back to "full capacity." The figure was later revised down to 57 flights.
A flight that was due to leave Phoenix at 7:50 p.m. PT (10:50 p.m. ET) en route to Burbank, Calif., pushed away from the gate, then sat for an hour before passengers were allowed to deplane, said NBC News producer John Boxley, who was on the plane.
The passengers later reboarded and Boxley said they were told they would take off soon.
NBC'sIan Johnston and The Associated Press contributed to this report.