CHICAGO - 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 on Tuesday afternoon, 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,' Ms 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.

'The backup system is working and is processing flight plans but because there were so many it had to handle it caused some delays in the system,' Ms Jones said.

Ms Jones did not know how many flights were delayed or when the system would return to full operations. -- AFP