Southwest Airlines' website crashed Tuesday, preventing reservations bookings and online flight check-in during a hectic holiday travel week.

"Southwest.com recovery is underway," the airline said in an email statement. "Our technology teams are in the process of restoring our website to full functionality, including the ability for customers to check in and alter reservations online."  Southwest did not identify the cause, or say when the problem would be fixed.

Passengers affected by the interruption and traveling through Dec. 21 can change their flight itineraries without paying a fee, the Dallas-based carrier said.  Customers can still check in at airports using kiosks, or at Southwest ticket counters "We appreciate our customers' patience as we work to restore the website," the statement said.