Airspace over the southern UK has been completely closed as a result of a computer failure.
The closure is in effect until at least 19:00, according to Eurocontrol.
UK air navigation service NATS says its main air traffic centre at Swanwick has suffered a “technical problem”.
“Every possible action is being taken to assist in resolving the situation and to confirm the details,” it adds.
Eurocontrol says the failure centres on Swanwick's flight-data computer server.