One of the busiest airports in the United Kingdom shut down Thursday morning after a drone sighting.

The incident started Wednesday evening and left more than 100,000 passengers stranded after their planes were grounded at Gatwick Airport.

Gatwick Airport said in a Twitter posting Thursday morning that “all flights remain suspended, due to ongoing drone activity around the airfield.” It went on to say there was “significant disruption, as a result of what appears to be a deliberate attempt to disrupt flights.”

On Thursday, the Sussex Police said on Twitter that they did not believe the incident was terrorism-related. They said they were trying to figure out who was operating the drone and were asking for information.

Officials went on to say that “public safety is paramount and we will take all available actions to disrupt this deliberate act.”

Travelers were expected to face even more delays for the busy holiday season as officials investigate the situation.

There was plenty of reaction on social media. @RonGonsalves2 wrote, “Humans planning to go to mars and here can’t find the drone.”