Air New Zealand is blaming its computer system crash on supplier IBM, which it says fell "well short of expectations".
An IT outage crashed airport check-in systems, as well as online bookings and call centre systems about 9am on Sunday, affecting more than 10,000 passengers and throwing airports into chaos.
Most systems were restored early on Sunday afternoon, but the passenger backlog did not clear until self check-in kiosks were up and running again about 3.30pm.
"We are sorry customers faced delays of up to two hours as we used manual processes for check in and boarding," Air New Zealand short haul airline group general manager Bruce Parton said.
He said the company appreciated the patience customers had shown, particularly as many were travelling with children at the end of school holidays."
The IT outage at the IBM-run central computer facility affected other businesses as well, he said.
"We are deeply disappointed by the performance of this supplier, who has fallen well short of the expectations we have on behalf of our customers," Parton said.
The outage would be investigated further tomorrow, he said.
Passengers at Wellington Airport said they faced long delays and criticised a lack of information from the airline.
"They haven't made that many announcements really," Judy, who was waiting there for her Christchurch flight, said.
Angela, who was waiting to fly to Hamilton, was also annoyed at the lack of information.
"It just goes to show how much we rely on technology," she said.
"When it goes down no one knows what the hell to do."
"It's just been chaos," an Air New Zealand staff member working at the check-ins said.
Parton would not comment about complaints of a lack of information relayed to passengers at Wellington Airport, but said: "that certainly hasn't been the case in Auckland".
The electronic system for checking people in was back up and running about 1.40pm, he said.
The airline had used manual check-in systems and opened about 10 extra counters while the system was down.
"It's just slow is the issues obviously for us, it's just a paper based system."
At midday passengers were facing delays of about an hour and a half, at 3.30pm they were about 1 hour 10 minutes.
Extra staff did not need to be brought in as many people, such as himself, had shown up to help.
The chaos may have left a few smiling - the carpark owners who had an unexpectedly busy Sunday with vehicles forced to stay for extended periods.