Drone sightings ground planes at Gatwick Airport located south of London

A major international airport in Britain was forced to ground flights after reports of drones flying over the airfield, the airport said Thursday.

Flights into Gatwick Airport, south of London, were diverted to other cities across the country while passengers waiting to take off faced long delays just days ahead of Christmas, the UK's Press Association news agency reported.

"Following reports of two drones flying over the Gatwick Airport airfield we have had to suspend flights while this is investigated," Gatwick Airport said in a statement late Wednesday night.

"We apologise to any affected passengers for this inconvenience but the safety of our passengers is our foremost priority." The runway has since reopened but passengers continue to face delays while airlines "catch up on the flight schedule", the airport said Thursday morning.

Sussex Police was investigating the incident, it added.

Gatwick is the eighth-busiest airport in Europe and sits behind Mumbai as the world's busiest single-runway air hub.

It serves more than 228 destinations in 74 countries for 45 million passengers a year.

Under British legislation, drones cannot be flown near aircraft or airports, or at an altitude of over 400 feet (122 metres).