Around half of flights in Europe could be delayed due to a fault with an air traffic management system.
Eurocontrol warned that around 15,000 flights may be disrupted after it suffered a computer failure.
The issue affected a system used to manage air traffic by analysing demand and capacity.
Flight plans submitted to Eurocontrol before 11.26am were lost and airlines were asked to resubmit the information.
A spokesman for the organisation, which has 41 member states including the UK, said: “We are very sorry about all the disruption and are working hard to get operations back to normal.
“We are expecting that our system should be fully up and running tomorrow.”
There are no safety implications as a result of the computer failure, the group added.
Luton-based carrier easyJet said in a statement: “Due to an earlier flight failure of the Eurocontrol flight planning system, easyJet like other airlines experienced delays to some departing flights.
“Ten flights were delayed between one hour and three hours with 16 flights delayed as a knock-on effect caused by the initial delays. EasyJet will operate 1,598 flights today.
“For passengers on delayed flights we are providing the latest information and refreshments as required.
“We understand that the issue has now been identified and we are working with Eurocontrol to minimise any further disruption for our passengers.
“While the situation is outside of its control, easyJet apologises for any inconvenience caused by the delays.”
The UK’s busiest airport, Heathrow, said there was no impact on its operations.
Some 59% of departing flights at Gatwick were delayed between 3pm and 4pm, according to airline data company FlightStats.
A spokeswoman for the West Sussex airport was unable to immediately confirm that the disruption was caused by the system failure.
UK air traffic control provider Nats said the problem was unconnected to its planned airspace capacity restrictions which come into force on Wednesday as a new technology system is introduced.