An Amadeus spokesperson told iTWire in response to queries that the systems had now recovered and were functioning normally.
Carriers like Qantas, British Airways, Lufthansa and Cathay Pacific were among the airlines affected. KLM had to delay the departure of at least 24 flights, according to a Bloomberg report.
Amadeus' Altea passenger-service system, which helps manage flight reservations, inventory and departure control, is used by more than 130 airlines globally.
"Due to a technical issue affecting check-in systems of some airlines, the check-in process may take longer than usual," the airport said.
#ADVISORY: Due to a technical issue affecting check-in systems of some airlines, the check-in process may take longer than usual...— Changi Airport (@ChangiAirport) September 28, 2017
#ADVISORY: ... Manual boarding passes have to be issued. We appreciate your patience in this matter. Thank you.— Changi Airport (@ChangiAirport) September 28, 2017
The Amadeus spokesperson said: "We experienced a network issue that caused disruption to some of our systems. As a result of the incident, customers experienced disruption to certain services.
"The incident was related to our internal infrastructure. It was triggered by an issue in a faulty switch during network maintenance. The incident was not related to any security issue."
The spokesperson said Amadeus technical teams had taken immediate action to identify the cause of the issue and mitigate against the impact on customers.
"Amadeus regrets any inconvenience caused to customers," the spokesperson added.
Amadeus has about 43% of the booking systems market, with Sabre and Travelport Worldwide being the other big players.
iTWire also contacted Qantas for comment but the airline has yet to respond.