A man and woman have been arrested over the "criminal use of drones" over London's Gatwick Airport, which saw all flights cancelled and hundreds of thousands of travellers delayed days before Christmas.

The Sussex Police today confirmed the arrests had been made as a part of ongoing investigations launched following the shutdown of the airport.

“As part of our ongoing investigations into the criminal use of drones which has severely disrupted flights in and out of Gatwick Airport, Sussex Police made two arrests just after 10pm on 21 December," a statement said.

“Our investigations are still on-going, and our activities at the airport continue to build resilience to detect and mitigate further incursions from drones, by deploying a range of tactics.

“We continue to urge the public, passengers and the wider community around Gatwick to be vigilant and support us by contacting us immediately if they believe they have any information that can help us in bringing those responsible to justice.

“The arrests we have made this evening are a result of our determination to keep the public safe from harm, every line of enquiry will remain open to us until we are confident that we have mitigated further threats to the safety of passengers."

Earlier, all flights resumed at the airport following a second, temporary shutdown due to another drone sighting.

The airport said in a statement that "military measures" in place at Britain's second-busiest airport made it safe to resume flight operations.

It said take-offs and landings had been suspended earlier on Friday - for roughly 80 minutes - as a precautionary measure while an investigation was under way.

An airport spokeswoman said there had been a confirmed sighting of a drone.

Flights at Gatwick, which serves over 43 million passengers a year, had been shut down all of Thursday and for several hours on Wednesday evening due to drone sightings.

The shutdown came roughly 11 hours after flights resumed Friday morning (local time) at Britain's second-busiest airport. (AAP)

The shutdowns have caused chaos over the holiday period.

Britain deployed unidentified military technology to guard the airport against what transport minister Chris Grayling said were thought to be several drones.

"This kind of incident is unprecedented anywhere in the world," he said.

A police helicopter flies over the runway at Gatwick Airport, London, as the airport remains closed with incoming flights delayed or diverted to other airports, after drones were spotted. (AAP)

The motivation of the drone operator, or operators, was unclear.

Police said there was nothing to suggest the crippling of one of Europe's busiest airports was a terrorist attack.

Gatwick's drone nightmare is thought to be the most disruptive yet at a major airport and indicates a new vulnerability that will be scrutinised by security forces and airport operators across the world.

The shutdowns have caused chaos over the holiday period. (AAP)

The army and police snipers were called in to hunt down the drones, thought to be industrial-style craft, which flew near the airport every time authorities tried to reopen it on Thursday.

No group has claimed responsibility publicly for the incident and police said there was no evidence another state was involved.

Sussex Police assistant chief constable Steve Barry said they were keeping an open mind about who was responsible.

"In terms of the motivation, there's a whole spectrum of possibilities, from the really high-end criminal behaviour that we've seen, all the way down to potentially, just individuals trying to be malicious, trying to disrupt the airport," he said.

The defence ministry refused to comment on what technology was deployed, but drone experts said airports needed to deploy specialist radar reinforced by thermal imaging technology to detect such unmanned flying vehicles.

Other ways to tackle them is typically by frequency jamming that can disable or disrupt control signals and the GPS signals that allow the drones to navigate.

People look at the arrivals board at Gatwick airport, as the airport remains closed after drones were spotted over the airfield. (AP)

The drone sightings caused misery for travellers, many sleeping on the airport floor as they searched for alternative routes to holidays and Christmas family gatherings.