United Airlines experienced worldwide flight delays Thursday evening for several hours due to a computer issue, the Chicago-based airlines confirmed.

"Earlier tonight we experienced an issue with our weight reporting system, which caused system wide flight delays," United said in a statement. "We have resolved the issue and are working to get customers to their destinations as soon as possible. We apologize for the inconvenience."

United did not provide a figure on the number of flights affected, but a spokeswoman told ABC News a "small number" of flights were affected "given the overnight timing." According to United's website, it has 4,550 daily departures.

The delays also created long lines at airports across the country, particularly along the West Coast.

The computer issue reportedly forced tickets agents at Los Angeles International Airport to issue paper tickets and manually check-in passengers on a sheet of a paper as they boarded aircrafts.

The airline's website, united.com, and its app were also temporarily down.

Some flights filled with passengers were also forced to remain on the tarmac after arriving, since since there were no open gates.