Two drones were first spotted flying above the runway at 9pm on Wednesday (December 19).
Click here for our live blog on the chaos at Gatwick Airport.
The airfield was closed at 9.02pm while police and airport security investigated and was reopened at 3.10am on Thursday (December 20).
However, further sightings of drones in the vicinity forced the runway to be closed again from 3.45am, according to Gatwick Airport.
Security staff at the airport are currently working alongside Sussex Police to investigate the sighting.
In a statement, Gatwick Airport said: "Unfortunately, this has led to a number of flights being diverted to other airports and all flight arrivals and departures are currently suspended from Gatwick.
"We advise anyone travelling today to contact their airline for the status of their flight before travelling to Gatwick this morning. If you are meeting someone from a flight, please check our live flight information for up to date about that flight.
"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.
"We apologise to any affected passengers for this inconvenience but the safety of our passengers and all staff is our number one priority."
At 7.40am Gatwick Airport tweeted: "Flights to and from Gatwick remain suspended, due to drone activity.
"Please do not travel to the airport without checking with your airline first. We're sorry for the inconvenience today, but the safety of our passengers and staff is our no.1 priority."
Ciara Martin, a teacher from Surrey, who was due to fly to Salzburg, Austria, at 7.05am described the scene inside the airport as 'mental'.
She said no flights are leaving yet and the airport is filling up.
Eurocontrol, the European air traffic management group, said the runway would remain closed until 10am.
Chris Woodroofe, Gatwick Airport's chief operating officer, told the BBC around 2,000 flights had been unable to take off which affected 10,000 passengers.
The law states it is illegal to fly a drone within 1km of an airport or airfield boundary.
Have you been affected by this morning's disruption? Email [email protected] to speak to one of our reporters.