Germany's Munich airport reopened on Friday after shutting overnight due to drone sightings that forced the cancellation or diversion of dozens of flights on the eve of a national holiday and heightened concerns about the vulnerability of critical infrastructure in Europe.

Axar.az reports, citing Reuters, as operations resumed early on Friday morning, a Reuters witness saw passengers checking in for a flight to Varna in Bulgaria, and the departure board showed only a few flights had been cancelled. A flight from Bangkok was the first of the day to land at around 5:25 a.m. (0325 GMT), according to the airport's website.

The airport said several drone sightings late on Thursday evening had forced air traffic control to suspend operations, leading to the cancellation of 17 flights and disrupting travel for nearly 3,000 passengers, who were provided with camp beds, blankets and food.

Another 15 arriving flights were diverted to other cities including Stuttgart, Nuremberg, Vienna and Frankfurt, the airport said.

The drones were sighted in the late evening above the airport, a police spokesman told newspaper Bild. But because it was dark, the size and types of the drones could not be determined, he added.