Passengers have reported long queues and delays after a worldwide glitch in the software used for checking in.
Online check-in system Amadeus Altea crashed, afftecting125 airlines.
Lufthansa, Air France and Southwest Airlines all reported check in delays due to the outage.
Several major airports were affected including Singapore's Changi Airport, Melbourne Airport and Charles De Gaulle in Paris.
Airports tried to minimise the error with Heathrow describing it as a "momentary IT glitch" and Gatwick referring to the issue as "intermittent" problems.
Travellers were however not impressed at delays, many taking to Twitter to express dissatisfaction.
Amadeus Software, the Spanish travel company behind the glitch, said that the disruption was due to a "network issue".
In a statement issued after service resumed, the company expressed disappointment over the outage.
"Our technical teams took immediate action to identify the cause of the issue and mitigate against the impact on customers. Amadeus regrets any inconvenience caused to customers," it said.
There are no reports of New Zealand airports being affected.