GATWICK AIRPORT, United Kingdom (AFP, REUTERS) - Britain's Gatwick Airport reopened on Friday (Dec 21) after dozens of drone sightings wrought travel chaos for hundreds of thousands of Christmas travellers in a cat-and-mouse game with police snipers and the army.

After the biggest disruption at Gatwick, Britain's second busiest, since a volcanic ash cloud in 2010, Gatwick said its runway was open and that a limited number of aircraft were scheduled for departure and arrival.

"Gatwick's runway is currently available and a limited number of aircraft are scheduled for departure and arrival," the airport said.

"Gatwick continues to advise passengers to check the status of their flight with their airline before travelling to the airport as departures and arrivals will be subject to delays and cancellations."

Flights were halted at 9pm local time (5pm Singapore) on Wednesday after two drones were spotted near the airfield. It is illegal to fly drones within 1km of a British airport boundary, punishable by five years in prison.

Police and airport authorities believe they were being flown in a deliberate act to disrupt the airport.

The unusually large drones had been spotted near the airfield more than 50 times over the 24-hour period, police said Thursday night.

"We think it may have been adapted and developed," said Detective Chief Superintendent Jason Tingley of the devices, adding officers were reviewing CCTV footage to identify the make and model.

The runway closure stranded tens of thousands of travellers days before Christmas - and prompted the unusual military operation.

Specialist equipment has been deployed by the Ministry of Defence to Gatwick airport to assist Sussex Police.

"We are there to assist and do everything we can," Defence Secretary Gavin Williamson told Sky News television, declining to give the troops' exact role and adding that it followed a request from local police.

Passenger Ani Kochiashvili had been bound for Georgia but spent six hours overnight sitting on a plane with her children.

"I'm very annoyed because I'm with two kids, a three-month-old and three-year-old," she told Reuters by phone among thousands camped in the terminal.

"They require a lot of space and food and changing and all that, and the airport is crazy busy so it's challenging."

Gisele Fenech, 43, who was travelling to Malta, was among those stranded at the airport.

"We're meeting family and it's my daughter's birthday today so it's gone all wrong. We've been looking forward to this for so long," she told AFP.

"Everyone's trying to get home for Christmas."

'IT'S CHILDISH'

Gatwick, around 50km south of the British capital, is the eighth-busiest airport in Europe and sits behind Mumbai as the world's busiest single runway air hub.Inbound flights were diverted to other airports, including Paris, while passengers waiting to take off faced gruelling delays as airlines cut services.

Easyjet, Gatwick's biggest operator, said it had cancelled all its flights in and out of the hub Thursday.

Transport Secretary Chris Grayling said overnight restrictions would be lifted at some airports to help ease the situation.

Some 10,000 passengers were affected on Wednesday night, and a further 110,000 who had been due to either take off or land at the airport on 760 flights Thursday.

Gatwick said it anticipated disruption to continue into Friday.

Musab Rashid, 22, who was going to Copenhagen, said: "It's wrong, it's childish of them to do this, because it's affected more than 100,000 people".

'HIGHLY TARGETED ACTIVITY'

Two drones were first spotted flying over Gatwick at around 9pm local time (5pm Singapore) on Wednesday. The airfield briefly reopened at 3am on Thursday, but had to be closed again following further sightings through the day.

Gatwick CEO Stewart Wingate said the incident was "a highly targeted activity which has been designed to close the airport and bring maximum disruption in the run up to Christmas".

Gatwick's chief operating officer Chris Woodroofe described one of the drones as a heavy industrial model. "We are working very closely with the police and the security services to try to resolve this for passengers," he said, adding "as soon as we can we will" reopen the runway.

Richard Parker, head of air traffic management technology firm Altitude Angel, said this was the first time a major airport had been hit by such a sustained and deliberate incursion into its airspace.

"It's sophisticated, not from a technology side, but it's organised. People have charged lots of batteries, and are deliberately trying to avoid being caught, probably by driving around to different locations," he told Reuters. "It really is unprecedented."

Drone expert Peter Lee of Portsmouth University said he and others had been anticipating the disruption. "One of my concerns about today is that it may well encourage copy-cat incidents because you can achieve a high amount of disruption for a very, very low cost," he said.

A cat-and-mouse manhunt is under way to catch those operating the drones, with more than 20 police units and dozens of officers from two local forces deployed.

NO TERROR LINK

Police superintendent Justin Burtenshaw said there was no terror motive. "We believe this to be a deliberate act to disrupt the airport. However, there are absolutely no indications to suggest this is terror-related," he said. He added: "Each time we believe we get close to the operator, the drone disappears; when we look to reopen the airfield, the drone reappears."

British Prime Minister Theresa May said she sympathised with passengers and vowed action.

"We will continue to work with the Gatwick authorities and police will be working... in order to bring this to a close," she said at a press conference in London.

Under a new British law, drones cannot be flown near aircraft or within a kilometre of an airport, or at an altitude of over 122m.

May warned the perpetrators they could face up to five years in prison for endangering an aircraft under recently passed legislation.

"We're consulting on further aspects of this including further police powers," she added.

Gatwick serves more than 228 destinations in 74 countries for 45 million passengers a year.

With a surge in public enthusiasm for drones, there has been an increase in near-collisions by unmanned aircraft and commercial jets in recent years.

The number of near misses between private drones and aircraft in Britain more than tripled between 2015 and 2017, with 92 incidents recorded last year, according to the UK Airprox Board regulator.