Gatwick announced that the runway had reopened at about 3am - but just 45 minutes later it was shut again.
Airlive.net, a website run by aviation enthusiasts that collects and displays real-time flight data, said all incoming flights to Gatwick were being diverted to other United Kingdom airports, like Manchester and Birmingham, and as far away as Paris and Amsterdam.
Two drones were spotted flying over the airfield at about 9.03pm this evening, with officials saying there had been further sightings since.
Early morning services between Jersey and Gatwick have been affected, but passengers are being advised to check in as normal.
Sussex Police launched an investigation and Gatwick promised to reopen the runway following "suitable reassurance".More news: Rocky Fielding knocked down four times in defeat to Saul 'Canelo' Álvarez
Luton Airport worker Adam Webster, who said he was forced to work an extra five hours until 4am due to diverted flights, offered lifts home to affected peoples living nearby.
According to the BBC, "Two of the unmanned devices were reportedly spotted near a runway, leading to delays and diversions as flights were suspended". Flying a drone within 1km of an airport or airfield boundary was made illegal in Britain at the end of July.
A spokeswoman added that airlines were working to provide hotel accommodation or transport for those whose flights were diverted.
Gatwick have stopped all arrivals and departures due to a drone, we've been told.
The airport has issued a warning, suggesting that people departing or picking someone up from Gatwick check the status of their flights.
He later added: "Update".