Airline customers have been hit with major disruption after computer check-in systems failed across the globe.
Frustrated passengers reported problems at London Gatwick, Heathrow, Charles de Gaulle in Paris and Reagan Airport in Washington DC.
Travellers in Singapore, Zurich, Melbourne and Johannesburg also appeared to be affected on Thursday morning after firms using Amadeus Altea software were hit with issues.
The software is used by 125 airlines across the globe both in airports and online.
One Southwest Airlines customer, who faced delays in Washington, tweeted: “Delays for travelers on Southwest Airlines at Reagan Airport. Computers at terminals are down. Follow @drgridlock for more.”
An Air France passenger added: “@CDG @airfrance now at #CustomerService the booking system is down waiting now for more than 100 minutes.”
A spokeswoman for Heathrow Airport told the Standard that a "small number of airlines" were experiencing "intermittent issues with their check-in desks around the world".
She said passengers were still able to check-in at the London hub but may face delays at Terminal 2, 3 and 4.
The spokeswoman added: "We are working closely with our airlines to help resolve the issue as quickly as possible. We apologise for any inconvenience this may cause.”
Images posted on social media showed huge queues at check-in desks across the world following what Gatwick Airport described as an “IT glitch”.
A spokeswoman for Gatwick said airlines which used Alea software had been affected.
The airport was unable to confirm which airlines were affected but told the Telegraph around 11am: “Things are back up and running after a momentary IT glitch.”
It was not immediately clear if the issue had been resolved at all airports.
Amadeus told the Standard just before 4pm that the issue had been resolved and confirmed it was not caused by a data or security breach.
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A spokeswoman said: "Amadeus can confirm that our systems are recovered and are now functioning normally. During the morning, 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.
"Amadeus technical teams took immediate action to identify the cause of the issue and mitigate against the impact on customers and regrets any inconvenience caused to customers.”