British military was called in on Thursday to provide assistance to police over Gatwich drone disruption, which is reported to have left thousands of Christmas holidaymakers to face "several days" of problems at the London airport.

The travel chaos were caused by drones over the runway, the airport's chief operating officer, said Christopher Woodroofe, adding that both inbound and outbound flights have been stopped in the wake of the disruption.

"Realistically if we do reopen today, what the airlines will seek to do is to deal with the passengers who are on site and to prepare for an operation tomorrow morning where we repatriate passengers who are in the wrong place," he said.

The spokeswomen for British Prime Minister Theresa May said Thursday that those flying the drones, which has forced the airport to shut its runway, were "irresponsible and completely unacceptable" and voiced sympathy for people having their travel plans upset just days before Christmas.

London Gatwick's runway has been shut since Wednesday night, when two devices were seen flying over the perimeter fence.

Local police said the incident was not terror-related.

The airport said 110,000 passengers on 760 flights were due to fly on Thursday.

Police were still hunting for the drone operator after another device was reported Thursday morning.

The shutdown, which started Wednesday night, came as two drones were spotted flying over the perimeter fence and into where the runway operates from.

The runway briefly reopened at early Thursday but was closed again amid a further sighting of drones.