Passengers flying via London's Gatwick Airport will face at least another 24 hours of disruption after several drone sightings forced Britain's second-busiest airport to shut its runway, causing delays to thousands of Christmas travellers.

Key points: Planes were unable to depart, and flights scheduled to land at Gatwick were rerouted

Planes were unable to depart, and flights scheduled to land at Gatwick were rerouted Flight disruptions are likely to last for more than 24 hours as runways remain closed

Flight disruptions are likely to last for more than 24 hours as runways remain closed Near-collisions between commercial jets and unmanned craft have increased in recent years

Planes were unable to depart after the drones were spotted, while a number of flights scheduled to land were diverted to other airports, Gatwick said in a statement.

Police said they believed the actions were deliberate and more than 20 units were searching for the drone operators.

The airport had expected to handle about 115,000 passengers on Thursday.

There were 92 near-misses between private drones and commercial jets last year. ( Reuters: Toby Melville )

"Public safety is paramount and we will take all available actions to disrupt this deliberate act," Sussex Police said in a statement. "There are no indications to suggest this is terror-related."

Gatwick's chief operating officer Chris Woodroofe could not say when flights would resume and warned that the knock-on effects from the airport closure would last for more than 24 hours.

Mr Woodroofe described one of the drones as a heavy industrial drone.

"It's definitely not a standard, off-the-shelf type drone," he said on BBC radio.

"Given what has happened I definitely believe it is a deliberate act, yes."

Gatwick apologised on Twitter to affected passengers, adding that safety was its "foremost priority".

An increase in near-collisions by unmanned aircraft and commercial jets has fuelled safety concerns in the aviation industry in recent years.

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

There were multiple reports of drone sightings since the initial report of two drones at 9:03pm on Wednesday (local time), Gatwick said.

"We also have the helicopter up in the air but the police advice is that it would be dangerous to seek to shoot the drone down because of what may happen to the stray bullets," Mr Woodroofe said.

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Some passengers took to Twitter to express their annoyance over the situation.

"I have two tiny children on board and a hotel room at Gatwick to get to," one passenger whose flight was redirected complained to British Airways on Twitter.

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The airline said earlier that the situation was not within its control.

Gatwick is 50 kilometres south of London and competes with Europe's busiest airport, Heathrow, 32 kilometres west of London.

"Our airlines are working to provide affected passengers with hotel accommodation or transport passengers landing at other airports to Gatwick by other means, and Gatwick staff are looking after passengers in our terminals," the airport said.

Under British law it is illegal to fly drones within 1 kilometre of an airport boundary. The offence is punishable by up to five years in prison.