London: Update: Passengers on a plane at London's Heathrow airport have been told that "things are starting to move", a witness told Reuters, after a drone sighting halted departures at Europe's biggest airport.
Transport minister Chris Grayling said in a tweet that the military were preparing to deploy equipment similar to that used at Gatwick last month during similar disruption if it proved necessary.
Flights from London's Heathrow airport were halted on Tuesday after the airport said there had been sightings of a drone flown near Britain'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."
Arriving planes however are continuing to land at Heathrow.
The incident comes just over two weeks after drone sightings at Gatwick, Britain's second biggest hub, caused travel misery for tens of thousands of people after flights were suspended over three days.
Gatwick has since said it has invested in anti-drone technology, while Heathrow said that it would do so.
In response to the chaos at Gatwick, Transport Secretary Chris Grayling on Monday told parliament that drone exclusion zones around British airports were being extended and operators will have to register.
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.
Grayling said the disruption at Gatwick between December 19 and 21 was "deliberate, irresponsible and calculated, as well as illegal".
The exclusion zone around airports is currently one kilometre (half a mile) and this will be extended to five kilometres.
From November 30 this year, operators of drones weighing between 250g and 20kg will also have to register and take an online pilot competency test.