Drone sightings at Germany's Munich airport have led to the cancellation and diversion of dozens of flights on the eve of a national holiday, leaving nearly 3000 passengers stranded, and authorities say they are investigating the incident.

The overnight disruption is the latest in a series of similar incidents that have rattled European aviation, raising concerns about deniable hybrid attacks on Ukraine's European allies, possibly directed by Russia.

As airport 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 after 5am on Friday, according to the airport's website.

The airport said several

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