A computer glitch caused mass delays at airports across the United States, authorities said on Tuesday.

The computer system that the Federal Aviation Administration uses to process flight plans at six major airports crashed around 1pm on Tuesday, and delays soon approached two hours.

Flights already in the air were not affected by the problem, FAA spokeswoman Tammy Jones told AFP.

"There is no safety issue at all — it's an efficiency issue," Jones said.

"We are investigating what the problem was, and in the meantime we're managing the system and working with the airlines to make sure everything works as efficiently as we can have it work at this time."

The airports affected by the system failure were in: Atlanta, Georgia; Boston, Massachusetts; Baltimore, Maryland; Charlotte, North Carolina; and two in Chicago, Illinois.

A slower backup system was able to process the flight plans and the glitch was soon identified, the FAA said.

All but two airports were back to normal traffic patterns by 7pm although storms in Texas and New York added further complications to the air traffic system.

AFP