The British Army has deployed "specialist equipment" to Gatwick Airport as the travel chaos caused by drone activity shows no sign of abating.
It comes as Easyjet has cancelled all of its flights from Gatwick for the rest of the day.
The airline, the biggest operator at the airport, said there was "no indication" when Gatwick would reopen.
Tens of thousands of passengers on several airlines have been disrupted by drones flying over the airport.
In a tweet, the Ministry of Defence (MoD) said Defence Secretary Gavin Williamson had confirmed the military deployment.
He said: "The armed forces have a range of unique capabilities and this isn't something we would usually deploy but we are there to assist and do everything we can so that they are in a position to open the airport at the earliest opportunity."
Officials from various government departments have been meeting and the prime minister is being kept informed.
Theresa May's spokesman said: "This is a serious incident, it's causing widespread disruption for passengers.
"The intention, obviously, is that it should be brought to a close as soon as possible."
Sussex Police said the drone activity was not terror-related but was a "deliberate act" of disruption, using "industrial specification" drones.
Gatwick chief executive Stewart Wingate agreed it was a "highly targeted activity" and added: "It cannot be right that drones can close a vital part of our national infrastructure in this way. This is obviously a relatively new technology and we need to think through together the right solutions to make sure it cannot happen again."
He is still "not in a position to say when it will be safe to reopen the airport".
About 110,000 passengers on 760 flights were due to fly on Thursday, but 633 flights were cancelled.
Transport Secretary Chris Grayling said: "We'll do everything we can to ensure that if Gatwick is not open again quickly that we can get [passengers] away from other airports."
He could not confirm whether the perpetrators were close to being caught but added: "There's a huge amount of effort going on - we've got up-to-date technology, we've brought special technology into Gatwick to try and track this down.