Heathrow is among several European airports hit by a cyber-attack affecting an electronic check-in and baggage system.
The airport warned of possible delays due to a "technical issue" affecting software provided by Collins Aerospace to several airlines.
Brussels Airport said a cyber-attack on Friday night meant passengers were being checked in and boarded manually, while Berlin's Brandenburg Airport also reported longer waiting times due to the problem.
RTX, which owns Collins Aerospace, said it was "aware of a cyber-related disruption" to its system in "select airports" and that it was working to resolve the issue as quickly as possible.
The company added: "The impact is limited to electronic customer check-in and baggage drop and can be mitigated with manual check-in operations."
