Frankfurt’s international airport, Germany’s busiest, was shut down for nearly two hours Monday after a drone was spotted near the facility, German federal police said. A pilot reported the drone over the southern part of the airport around 11:15 a.m. and the airport was shut as police searched the area with the support of a helicopter.

Police tweeted that the airport was reopened at 1 p.m. but the investigation was continuing.

Several flights were cancelled or rerouted, among them a plane with the governor of the western German state of North Rhine-Westphalia, Armin Laschet, who was returning from a visit to Israel.

Only a few weeks ago, Frankfurt airport had to be shut down for about an hour because of a drone sighting. In 2019, some 28 drone sightings were reported at Frankfurt.