One of the UK's busiest airports suspended or diverted all flights after drones were seen over its airfield.

The disruption at Gatwick Airport, which is 30 miles south of London, started around 9 p.m. local time Wednesday after a pair of drones were spotted, according to the BBC. Gatwick is Britain's second busiest airport.

The runway remained closed until 3 a.m. and then was shut down again 45 minutes later after "a further sighting of drones." It was still closed as of Thursday evening, and police are hunting for the drones' operator, Chris Woodroofe, Gatwick's chief operating officer, told the BBC.

The military has also been dispatched to assist police, Defence Secretary Gavin Williamson told reporters.

Sussex Police don't think the drones are part of a terror attack, but they're seeking the public's help to identify the operator and they suspect that devices are of "industrial specification."

It's illegal to fly a drone within 1 kilometer (0.6 mile) of an airport or airfield boundary, and you can't fly it above 120 meters (400 feet) where the likelihood of an aircraft hitting it increases.

Around 110,000 passengers on 760 flights were due to use the airport on Thursday, Gatwick told the BBC, and some overnight flights were diverted to Paris and Amsterdam.

"We anticipate disruption to continue throughout the day and into tomorrow. Any passengers due to fly today or tomorrow should not set off for Gatwick without checking flight information with their airline," the airport said in an updated Thursday release.

"We are extremely disappointed that what appears to be deliberate action is affecting journeys at this important time of year. We are working tirelessly with our airlines to put plans in place to recover our operation once given the go-ahead that our runway can reopen."

Gatwick didn't respond to a request for further comment.

In August, Gatwick was forced to post flight information on white boards after its digital screens failed due to an IT glitch.

First published at 2:59 a.m. PT; updates as the situation develops.

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