LONDON (AP) Flights are being delayed at Britain's busiest airports because of a technical problem at the country's main air traffic control center.

National Air Traffic Service said it was having a problem switching between nighttime and daytime operations at its control center in Swanwick, southern England. It said: "This may result in some delays, for which we apologize."

It said technicians were trying to fix the problem.

Heathrow Airport Europe's busiest is showing delays of an hour or more on many morning flights Saturday.

London's Stansted airport said departing flights were seeing delays of between 30 minutes and 2 hours because of restrictions on air space and the flow of planes. Gatwick airport said 20 percent of flights were being delayed.