Almost 15,000 flights could be delayed after a failure in Europe’s air traffic co-ordination system.
The European Organisation for the Safety of Air Navigation said almost 15,000 scheduled flights in Europe “could have some delay”.
Contingency plans put in place have reduced the network capacity by another 10%, it said.
The problem is expected to be solved late on Tuesday evening.
The safety group, also known by its shorter name Eurocontrol, said there had been a failure in its Enhanced Tactical Flow Management System.
The system helps to manage air traffic by comparing demand and capacity of different air traffic control sectors.
Air traffic control itself has not been directly affected, and Eurocontrol said there “are no safety implications arising from this incident”.
“We have never had anything like this before,” a Eurocontrol spokesman told the AFP news agency.