An airport spokesman confirmed flights had been suspended while investigations take place at the site, the latest incident comes on the day fresh police powers to tackle drones were announced in the wake of the crisis that disrupted more than 1,000 flights at Gatwick in December.
London's Heathrow, Europe's biggest airport, launched a public consultation on Tuesday ahead of the construction of a third runway, and gave details on how it plans to mitigate noise disruption for locals from thousands of extra flights.
Heathrow served 78 million passengers in 2017, with 81 airlines flying to 204 destinations in 85 countries around the world.
"As a precautionary measure, we have stopped departures while we investigate".
'We apologise to passengers for any inconvenience this may cause'.
Departures at Heathrow were temporarily stopped after a drone was reported to have been sighted.
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Heathrow staff are working with the Metropolitan Police and all flights have been grounded "as a precaution", an airport spokesperson said.
Planes could come in to land on both runways at the same time during busy periods, Heathrow has proposed, to help maximise its capacity ahead of expansion.
Gatwick has since said it has invested in anti-drone technology, while Heathrow said that it would do so.
"The military are preparing to deploy the equipment used at Gatwick at Heathrow quickly should it prove necessary."
Chris Grayling announced on Monday this week that he is seeking changes to the law which would allow officers to rapidly respond to and thwart drone attacks, including the ability to search premises of suspects and require users to produce documentation similar to a driver's licence. Plane not going anywhere due to drones'.
The British government yesterday expanded drone-free exclusion zones around British airports from their previous 1km limit, to about 5km.