"Due to a global outage affecting IT systems of many organizations, the check-in process for some airlines at Changi Airport is being managed manually," operator Changi Airport Group said in a Facebook post Friday.
"We have worked with our airport partners to bring in additional resources to support the manual check-in process. At the same time, Changi Airport ground staff have been providing assistance to affected passengers."
The affected airlines had to handle check-in, including the issuance of boarding passes, manually, Channel News Asia reported.
Budget carrier Scoot announced on its Facebook page it has been facing disruptions to its flight-reservation system and check-in processes and some flight delays.
AirAsia, Jetstar and Cebu Pacific at terminal 4 were also disrupted.
One flight from Singapore was canceled on Friday while 40 others were delayed due to the outage, Straits Times reported.
Photos shared on social media showed passengers queuing up at check-in counters.
In the latest announcement on Saturday morning, Changi Airport Group said check-in operations at its airport have returned to normal for most airlines affected by Friday’s tech glitch.
"A small number of airlines still require check-in to be handled manually. Changi Airport is supporting these airlines with additional resources."
Many other airports around the world have also been affected by the massive outage.