A cyberattack disrupted operations at several major European airports on Saturday, including Brussels Airport and London’s Heathrow, causing flight delays and cancellations.

The attack targeted the service provider for the check-in and boarding systems on Friday evening, Brussels Airport said in a statement. As a result of the attack, only manual check-in and boarding were possible, the airport said.

“This has a large impact on the flight schedule and will unfortunately cause delays and cancellations of flights,” the airport said.

By 10:30 a.m. Saturday, 10 flights departing from Brussels Airport had been canceled and 17 were delayed by more than an hour, said Ariane Goossens, a spokesperson for the airport.

Heathrow said on its website that Collins Aerospace, which provides check-in and boarding systems for airlines across multiple airports, was “experiencing a technical issue that may cause delays for departing passengers.”

A spokesperson for Collins Aerospace said the company had become aware of a “cyber-related disruption” to their MUSE software in select airports and were “actively working to resolve the issue and restore full functionality to our customers as quickly as possible.”

“The impact is limited to electronic customer check-in and baggage drop and can be mitigated with manual check-in operations,” they added.

Berlin Brandenburg airport also reported longer waiting times at check-in “due to a technical issue at a system provider operating across Europe.”

Airports advised passengers to check their flight status before coming to the airport.