Mystery drone operator/s have grounded flights at the U.K.’s second largest airport, disrupting the travel plans of hundreds of thousands of people hoping to get away over the festive period.

The BBC reports that Gatwick Airport’s runway has been shut since Wednesday night on safety grounds, after drones were spotted being flown repeatedly over the airfield.

It says airlines have been advised to cancel all flights up to at least 16:00 GMT, with the airport saying the runway would not open “until it was safe to do so.”

More than 20 police units are reported to be searching for the drone operator/s.

The U.K. made amendments to existing legislation this year to make illegal flying a drone within 1km of an airport after a planned drone bill got delayed.

The safety focused tweak to the law five months ago also restricted drone flight height to 400 ft. A registration scheme for drone owners is also set to be introduced next year.

Under current U.K. law, a drone operator who is charged with recklessly or negligently acting in a manner likely to endanger an aircraft or a person in an aircraft can face a penalty of up to five years in prison or an unlimited fine, or both.

Although, in the Gatwick incident case, it’s not clear whether simply flying a drone near a runway would constitute an attempt to endanger an aircraft under the law. Even though the incident has clearly caused major disruption to travelers as the safety-conscious airport takes no chances.

Further adding to the misery of disrupted passengers today, the Civil Aviation Authority told the BBC it considered the event to be an “extraordinary circumstance” — meaning airlines aren’t obligated to pay financial compensation.

There’s been a marked rise in U.K. aircraft incidents involving drones over the past five years, with more than 100 recorded so far this year, according to data from the U.K. Airprox Board.

Aviation minister Baroness Sugg faced a barrage of questions about the Gatwick disruption in the House of Lords today, including accusations the government has dragged its feet on bringing in technical specifications that might have avoided the disruption.

“These drones are being operated illegally… It seems that the drones are being used intentionally to disrupt the airport, but, as I said, this is an ongoing investigation,” she told peers, adding: “We changed the law earlier this year, bringing in an exclusion zone around airports. We are working with manufactures and retailers to ensure that the new rules are communicated to those who purchase drones.

“From November next year, people will need to register their drone and take an online safety test. We have also recently consulted on extending police powers and will make an announcement on next steps shortly.”

The minister was also pressed on what the government had done to explore counterdrone technology, which could be used to disable drones, with one peer noting they’d raised the very issue two years ago.

“My Lords, technology is rapidly advancing in this area,” responded Sugg. “That is absolutely something that we are looking at. As I said, part of the consultation we did earlier this year was on counterdrone technology and we will be announcing our next steps on that very soon.”

Another peer wondered whether techniques he said had been developed by the U.K. military and spy agency GCHQ — to rapidly identify the frequency a drone is operating on, and either jam it or take control and land it — will be “given more broadly to various airports”?

“All relevant parts of the Government, including the Ministry of Defence, are working on this issue today to try to resolve it as quickly as possible,” the minister replied. “We are working on the new technology that is available to ensure that such an incident does not happen again. It is not acceptable that passengers have faced such disruption ahead of Christmas and we are doing all we can to resolve it as quickly as possible.”