Technology provider Amadeus has acknowledged "disruption to some of our systems" following a "network issue" earlier today.
"As a result of the incident, customers experienced disruption to certain services," says Amadeus, which highlights the "immediate action" taken by its technical teams "to identify the cause of the issue and restore services as quickly as possible".
That action is "ongoing" and services are "gradually being restored", adds Amadeus.
Flight delays have been reported among a number of airlines and airports.
Dutch airline KLM notes the "malfunction" affects all Amadeus users. These include sibling carrier Air France as well as KLM itself.
"KLM's booking system temporarily does not work properly and there are also problems with rebooking," notes the Dutch airline. "Previous issues at check-in have been resolved."
There have been flight delays as a result of the network failure, KLM confirms.