(CNN) -- A computer glitch forced Southwest Airlines to ground 250 flights, the company said early Saturday.
Flights already in the air were not affected by the glitch, which started late Friday night.
Most flights resumed takeoff early Saturday after the airline resorted to a backup system.
"Flights have started to depart, but employees are working through a manual process so their routine work flow is taking a bit longer," said Michelle Agnew, a spokeswoman for the airline.
"The manual process is involved because the team doesn't have access to all of the normal tools they would use to be able to communicate and dispatch flights."
Agnew said the glitch was in the internal system used to dispatch flights. It mostly affected planes on the ground that were scheduled to depart, she said.
All Southwest flights were affected, but because the glitch occurred late, most of the planes waiting to fly were limited to the West Coast, she said.
Major Southwest hubs in Phoenix, Las Vegas and Oakland, California, had grounded their flights.
Southwest has an estimated 3,400 flights daily.