United Airlines computer systems are back up and running, the airline announced in a twitter message at approximately 11 PM Pacific Time.

Our systems are up. We are in the process of resuming ops for UA, United Airlines said.

The airline experienced a major computer systems failure at approximately 5:15 PM Pacific Time.

According to United Airlines flight departure, airport processing and reservations systems were interrupted according to airline spokesman Scott O'Leary.

Planes were unable to take off and long lines were present at the airports, including San Francisco International Airport (SFO), due to the computer outage.

In addition, United's website was down for a period of time.