Some flights to and from the UK are facing delays because of problems affecting French air traffic control.
British Airways said an “outage” had affected flights travelling through French and Spanish airspace.
Easyjet said it was experiencing disruption due to a “partial failure of French air traffic control systems”.
Paris Airport tweeted that a “national computer failure related to the centralisation of flight plans” on Sunday morning was now resolved.
But it warned that delays are still expected.
National Air Traffic Services (NATS) said it does not know how many flights have been affected but said it is working with airlines in the UK to try to minimise disruption.
Gatwick Airport urged passengers to check with airlines on the status of their flights before heading to the airport.
Easyjet said it would publish a list of flights it has been forced to cancel, adding that is was seeing “significant delays”.
British Airways urged customers to check the status of their flights online.
The airline said it expects disruption to services to France and Spain, as well as those which fly over these countries on the way to other destinations.
It said it would offer flexible rebooking options for passengers who want to change their dates of travel as a result of the disruption.