Flights at Britain's second busiest airport, London Gatwick, remained suspended on Thursday after several sightings of drones flying near its airfield, causing disruption to thousands of people travelling before Christmas.
Planes were unable to take off and a number of flights scheduled to land were diverted to other airports, Gatwick said, with the plans of at least 20,000 passengers already affected and thousands more facing disruption on Thursday and Friday.
Over 100,000 passengers a day fly to and from Gatwick Airport each day.
Gatwick's Chief Operating Officer Chris Woodroofe said police were looking for the operator of the drone.
"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," he told BBC radio.
"My advice to those passengers who are travelling today and tomorrow is to check their airlines websites before they travel to the airport," said Woodroofe.
He warned that the knock-on effects on flights in terms of delays and cancellations would be felt for at least the next 24 hours.
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 2103 GMT on Wednesday, Gatwick said. It said it required police reassurance before reopening the runway, which it briefly appeared to do around 0300 GMT before drones were spotted again.
"Police at Gatwick airport are continuing to assist airport security teams following a number of reports and sightings of drones in the vicinity of the airfield overnight on Wednesday and Thursday," Sussex Police said in a statement.
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
Gatwick is 50 km (30 miles) south of London and competes with Europe's busiest airport, Heathrow, 32 km (20 miles) west of London.