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.
"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.
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).