Domestic and international travellers are experiencing delays after a global reservations system used by Australian airlines crashed, disrupting flights around the country.

A spokeswoman said Qantas was one of a number airlines around the world affected when the global transaction processor experienced outages in one of its programs on Sunday.

The service provides check in, load control and inventory services to its clients, which include Qantas and other international airlines.

The spokeswoman said Qantas was now back on line, however there would continue to be delays.

"Everything is back on line for Qantas but there are one hour delays which will decrease throughout the day," the spokeswoman said.

She said domestic flights were delayed by about an hour and international flights faced delays of up to an hour.

Travellers took to the microblogging site Twitter to report chaos and long queues.

ABC personality Karl Kruszelnicki tweeted "big queues and Qantas domestic" and traveller Daz Martin reported "chaos at Adelaide airport Qantas check-in crashed".

A tweeter identified as Fake Qantas PR put a more topical spin on the situation, saying "If you're flying #qantas today, please be patient. Our systems are down. And no, it's not because we didn't pay our Carbon Tax bill.

AAP