The outage, which affected check-in and boarding systems, began at about 4:30pm but was fixed just after 7:30pm.
The system failure was linked to the Sabre software system used by the two airlines and airport staff were forced to use manual check-in processes.
Although the system is back online, resorting to manual processes has led to delays of about an hour, a spokesperson said.
However passengers are reporting flights are two hours behind and waiting areas at gates overcrowded.
Other passengers took to social media to report that they had been stuck on the tarmac for hours.
“Two and a half hours on the tarmac in Sydney. Where’s your back-up plan?” Mark Burston said.
“Been sitting waiting to board VA874 since 5:30 and not one announcement from the staff,” Ash Chin said.