Computer system glitches at United Airlines delay thousands of passengers

Computers glitches on United Airlines' computer systems on Thursday led to flight delays, leaving thousands of passengers stranded.

The carrier told NBC News early Friday that 63 flights were affected, but spokeswoman Maddie King later retracted the figure saying it was just "a small number of flights."

According to King, the first glitch, that hit United's luggage weighing systems, was resolved late Thursday, but another issue caused more delays before being resolved at 3 am. King however, denied knowledge of its nature and cause.

Passengers took to social media to vent their frustrations, and posted pictures and messages from San Francisco and Newark to Costa Rica and London.

According to commentators, the glitch appeared to not as big as the one involving United Airlines' computer systems in July that affected around 3,500 flights.

''Earlier tonight we experienced an issue with our weight reporting system, which caused system wide flight delays,'' the airline said in a statement on its Twitter feed late on Thursday in the US.

''We have resolved the issue and are working to get customers to their destinations as soon as possible. We apologize for the inconvenience.''

According to passengers, they had been forced to wait onboard planes or inside terminals as delays stretched over several hours.

''On the plane for more than an hour, away from the gate and no communication. What's happening?,'' one passenger tweeted.

In Paris, passengers complained as check-in lines grew for a flight to New York, a Reuters reporter said on Friday morning.

After the July incident United Continental Holdings said it had invested in backup plans.

However, in view of the recent outages, some experts and passenger groups question whether the airline industry had invested enough in technological infrastructure.