Passengers stuck at Heathrow expressed their frustration at having to wait to depart while the airport responded to the sighting.
In a statement, an airport spokesperson said: "We are now responding to a drone sighting at Heathrow and are working closely with the Met Police to prevent any threat to operational safety. They've only given us one update to say it was because of drone activity in departures". "We apologies to passengers for any inconvenience this may cause".
Flight departures have been suspended at London's Heathrow Airport following reports of a drone sighting.
A spokesperson for London's Metropolitan Police said they were called just after 5pm to "reports of a sighting of a drone in the vicinity of Heathrow Airport".
The force said "officers based at Heathrow are now investigating the reports with colleagues from (the) airport".
"We've been sitting on the runway at Heathrow for like an hour and a half", another person said.
"I have already spoken to both the Home Secretary and Defence Secretary and the military are preparing to deploy the equipment used at Gatwick at Heathrow quickly should it prove necessary". About 1,000 flights were cancelled or diverted, affecting 140,000 passengers.
This incident comes after operations at Gatwick Airport, about 30 miles southeast of Heathrow, were brought to a screeching halt amid the busy Christmas travel season because of drone sightings there.
Today, the British government announced a package of measures created to give police extra powers to combat drones.
Grayling said the government would also begin testing the use of counter-drone technology as part of its response to a consultation begun before December's disruption. Exclusion zones are now one kilometre around airports and will be extended to five kilometres.
Police will also be allowed to fine users up to £100 (112 euros, $128) for failing to comply when instructed to land a drone, or not showing registration to operate a drone.