Flights from London's Heathrow Airport were halted for about an hour on Tuesday after the airport said there had been sightings of a drone near Europe's busiest air hub.
"We are responding to a drone sighting at Heathrow," the airport said. "As a precautionary measure, we have stopped departures while we investigate. We apologise to passengers for any inconvenience this may cause."
London's Metropolitan Police said they had received reports of a drone near the airport at about 5.05pm on Tuesday, which they were investigating with airport authorities.
The airport confirmed about an hour later that take-offs had resumed. Flight tracker websites showed flights departing from 6.11pm.
London's second busiest airport, Gatwick, was severely disrupted in December when drones were sighted on three consecutive days, resulting in about 1,000 flights being cancelled or diverted and affecting 140,000 passengers.
The British army deployed unidentified military technology to guard the area, reassuring the airport that it was safe enough to fly.
Heathrow and Gatwick responded by ordering military-grade anti-drone defences worth "several million pounds".
Heathrow said earlier this month it was working closely with authorities including the police and looking at relevant technology to combat the threat of drones.