Large queues have formed outside Dublin Airport due to a fault with Aer Lingus' systems.
As the Irish Examiner reports, the airline has said its system is currently down and a team is working to resolve the issue as soon as possible.
Posting to Twitter, Aer Lingus said: "We apologise to our customers for any inconvenience caused in this period.
"We are working to resolve the connection issues as soon as possible."
The issue stems from a technical problem with the Cloud-based reservation and operational systems.
Delays and disruption to services are anticipated to last for several hours.
The Aer Lingus website is also down and is displaying a notice that says it is due to a scheduled upgrade.
"Our website is currently unavailable while a scheduled upgrade is in progress," the web page reads.
Dublin Airport has said Aer Lingus is experiencing an internal IT issue which is impacting check-in and boarding.
They asked passengers to co-operate with teams as work continues to resolve the problem.
Aer Lingus has been responding to frustrated passengers on Twitter.
It said that all passengers would be notified when an update has been confirmed.
People have been posting pictures of winding queues outside Terminal 2 this morning.
We apologise to our customers for any inconvenience caused in this period. We are working to resolve the connection issues as soon as possible.
— Aer Lingus (@AerLingus) September 10, 2022