The flying of drones at Gatwick, which has caused the runway to be closed, is “a deliberate act to disrupt the airport”, police said.
Tens of thousands of passengers are suffering travel chaos after all flights at the West Sussex airport were suspended.
The runway was closed at 9pm on Wednesday after two of the devices were seen near the airfield.
It was reopened at 3am on Thursday, but was shut again 45 minutes later after a further sighting of drones.
At 9.15am, the airport said there was “ongoing drone activity” and the runway remained closed.
Superintendent Justin Burtenshaw of Sussex Police said: “We believe this to be a deliberate act to disrupt the airport. However, there are absolutely no indications to suggest this is terror related.”
Some 10,000 passengers were affected on Wednesday night, and a further 110,000 were due to either take off or land at the airport on 760 flights on Thursday.