Munich Airport was temporarily shut down overnight after several drone sightings in the area, the latest mysterious drone overflights in the airspace of European Union member countries, officials said.

Germany’s air traffic control restricted flights at the airport shortly after 10 p.m. (2000 GMT) on Thursday and then halted them altogether, airport operators said in a statement. Seventeen flights were unable to take off, affecting almost 3,000 passengers, while 15 arriving flights were diverted to three other airports in Germany and one in Vienna, Austria.

Flights in and out of the airport resumed at 5 a.m. (0300 GMT), said Stefan Bayer, a spokesperson for Germany’s federal police at Munich airport. Authorities were not immediately able to provide any information about who was responsible for the overflights.

A statement from the airport early Friday said there had been “several drone sightings,” without elaborating. Bayer said it wasn’t immediately clear how many drones might have been involved. He said police, airline employees and “regular people around the airport” were among witnesses who reported the drone sightings.

After the closure of the runways, federal police deployed helicopters and other means to try to track down the drones, but no signs of them could be found, Bayer said.