Flights at Gatwick Airport have been suspended amid reports of two drones being flown over the airfield.
Passengers, who faced delays and diversions after the devices were seen near a runway, were warned disruption could continue into Thursday.
Those due to depart on Wednesday said planes were left stuck on the Tarmac, while inbound flights were diverted.
People going to Gatwick to travel or to meet relatives have been advised to check the status of their flight first.
A spokesman said the airport would update passengers once there had been “suitable reassurance that is it appropriate to re-open the runway”.
He apologised for any inconvenience and said Sussex Police was working alongside Gatwick staff to investigate the drone sightings.
According to the airport, the drones were first seen at 21:03 GMT on Wednesday, followed by “multiple reports” of sightings.
Kasia Jaworska told the BBC she had been travelling from Glasgow to Gatwick with her boyfriend when her flight was diverted to Luton.
After spending about two hours on the plane, she said the couple were put on a bus to Gatwick, where they had been due to fly to Istanbul.
Ms Jaworska said it was “strange” that two drones had led to the closure of the airport.
“You would imagine there would be better security in place and emergency action for something like that,” she said.
On social media, passengers spoke of flights being diverted to other UK airports, including London Heathrow, Luton and Manchester.
Rashna Havewalla said she and her fellow passengers were sat waiting inside their aircraft at Manchester.
Richard Hargreaves’ easyJet flight was redirected to Birmingham, with those on board waiting to fly back to Gatwick.
Honor Ireland said her flight had ended up at Stansted, but her car was parked at Gatwick.
Gatwick Airport said airlines were “working to provide affected passengers with hotel accommodation” or provide alternative travel options.
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