Major disruptions are being reported in airports around the world following the failure of computer check-in systems.

The mishap has struck some of the world’s busiest airports, including London Heathrow, London Gatwick, Zurich, Melbourne, Johannesburg, Changi in Singapore and Reagan National Airport in Washington, according to The Telegraph and the BBC.

Amadeus Altea said that a network issue hit its software in the early hours of Thursday morning, disrupting some of its systems. According to its website, more than 124 airlines use Amadeus’ technology.

“Amadeus technical teams took immediate action to identify the cause of the issue and restore services as quickly as possible,” the company said in a statement. “That action is ongoing with services gradually being restored. Amadeus regrets any inconvenience caused to customers.”

Heathrow Airport tweeted that a small number of airlines were experiencing problems across the world but that it was “working closely with them to solve the issue.”