London's airspace has been closed due to a computer failure, the European air control agency Eurocontrol said Friday.

Officials at London Heathrow Airport said there was a power outage at the NATS control center in Swanwick, England. Heathrow's statement gave no indication how long the situation was expected to continue.

The shutdown came at a busy time at the start of the weekend in a sprawling city with five commercial airports, including London Heathrow, Europe's busiest, as well as Gatwick, Luton, Stansted and London City Airports.

The statement said "flights are currently experiencing delays and we will update passengers as soon as we have more information."

The NATS control center said "a technical problem has been reported at Swanwick air traffic control center" and an incident response team has been mobilized.

"Every possible action is being taken to assist in resolving the situation and to confirm the details," the control center statement said.

At Heathrow, passengers on United flight 941 to Newark were told about the computer problem as they boarded at 1530 GMT (10:30 am EST). United gate staff said the plane would be loaded with passengers and head toward a runway in the hopes that the computer problem could be fixed.

Most passengers at Heathrow seemed unaware of the issue and no further mention was made during normal boarding.