The Metropolitan Police said they were called at around 1705 GMT and alerted to "reports of a sighting of a drone in the vicinity of Heathrow airport". A statement on the airport's Twitter account earlier said: "We are responding to a drone sighting at Heathrow and are working closely with the Met Police to prevent any threat to operational safety.
"As a precautionary measure, we have stopped departures while we investigate. We apologise to passengers for any inconvenience this may cause," it said. Arriving planes, however, continued to land at Heathrow. Transport Secretary Chris Grayling said "the military are preparing to deploy the equipment used at Gatwick at Heathrow quickly should it prove necessary".Some 81 airlines serving 204 destinations operate out of Heathrow, located west of London.