Thousands of passengers have been affected by drones flying over the UK’s second busiest airport’s runways.
London’s Gatwick Airport’s runway has been shut since Wednesday night, as devices have been repeatedly flying over the airfield.
Sussex Police said it was not terror-related but a “deliberate act” of disruption, using “industrial specification” drones.
About 110,000 passengers on 760 flights were due to fly on Thursday. Disruption could last “several days”.
The airport said it had advised airlines to cancel all flights up to at least 16:00 GMT, adding the runway would not open “until it was safe to do so”.
Those due to travel have been told to check the status of their flight, while Easyjet told its passengers not to go to Gatwick if their flights have been cancelled.
The shutdown started just after 21:00 on Wednesday, when two drones were spotted flying “over the perimeter fence and into where the runway operates from”.
The runway briefly reopened at 03:01 on Thursday but was closed again about 45 minutes later amid “a further sighting of drones”.
The airport said at about 12:00 a drone had been spotted “in the last hour”.
Gatwick chief operating officer Chris Woodroofe said: “The police are looking for the operator and that is the way to disable the drone.”
He said police had not wanted to shoot the devices down because of the risk from stray bullets.
He said it remained unsafe to reopen the airport after the drone had been spotted too close to the runway.
Mr Woodroofe said: “If we were to reopen today we will first repatriate passengers who are in the wrong place which could take several days.”
More than 20 police units from two forces are searching for the perpetrator, who could face up to five years in jail.
About 10,000 passengers were affected overnight on Wednesday and Gatwick said 110,000 people were due to either take off or land at the airport on Thursday.
Incoming planes were diverted to other airports including London Heathrow, Luton, Birmingham, Manchester, Cardiff, Glasgow, Paris and Amsterdam.
Crowds of travellers spent the morning waiting inside Gatwick’s terminal for updates, while others reported being stuck on grounded planes for hours.
A Gatwick spokeswoman said extra staff had been brought in and the airport was “trying their best” to provide food and water to those who needed it.
About 11,000 people are stuck at the airport, Mr Woodroofe said.
A number of flights bound for Gatwick were diverted to other airports overnight, including seven to Luton, 11 to Stansted and five to Manchester. Other flights have landed at Cardiff, Birmingham and Southend.
The Civil Aviation Authority said it considered this event to be an “extraordinary circumstance”, and therefore airlines were not obligated to pay any financial compensation to passengers.
It is illegal to fly a drone within 1km of an airport or airfield boundary and flying above 400ft (120m) – which increases the risk of a collision with a manned aircraft – is also banned.
Endangering the safety of an aircraft is a criminal offence which can carry a prison sentence of five years.
The number of aircraft incidents involving drones has grown dramatically in the past few years. In 2013 there were zero incidents, compared to almost 100 last year.
Civilian drones have grown popular as their price has fallen. Technological improvement has meant components are smaller, faster and cheaper than ever before.
The UK Airprox Board assesses incidents involving drones and keeps a log of all reports.
In one incident last year, for example, a pilot flying over Manchester saw a red “football-sized” drone passing down the left hand side of the aircraft.
In another, a plane leaving Glasgow narrowly missed a drone. The pilot, in that case, said the crew only had three seconds of warning and there was “no time to take avoiding action”.