Groups of unidentified drones prompted a busy German Airport to close briefly as authorities investigated.
Dozens of flights to and from Munich Airport were cancelled or delayed due to the mystery drones.
Thousands of passengers were affected by the closure, with local authorities adding that they still don’t know who or what was behind the drones. The airport has now reopened.
A spokesperson said: ‘Nineteen Lufthansa flights were affected, either cancelled or rerouted, because of the airport suspension.’
Last week, more suspicious drones were spotted over northern Germany on the very same night they were seen near a Swedish naval base.
Authorities in Schleswig-Holstein are investigating the prospect that the drones were up to espionage or sabotage, the interior minister said.
Drone activity in Denmark caused concern after the country’s busiest airport was forced to shut, wreaking havoc on travel as planes were grounded.
More drones were reported over the Aalborg, Sonderborg and Esbjerg airports and near the Skrydstrup airbase.
At least two more large drones were seen flying over the Karlskrona archipelago in southern Sweden, just six miles from the nearby naval base.
Schleswig-Holstein Interior Minister Sütterlin-Waack said state police are boosting counter-drone defences in coordination with Bundeswehr and neighbouring regions.
Where the drones spotted originated from and what is behind the flights remains unclear, but a number of drones were also spotted in the state in August.
The head of a global firm that provides sophisticated drone defences has said that he does not know of a fully-protected civilian airport.
Oleg Vornik, of DroneShield, warned that counter-measures are lacking at a time of Russian probing and sabotage across the UK and Europe.
The chief executive spoke at the end of a week when uncrewed aerial systems (UAS) caused Denmark’s busiest airport to close and were detected near a naval base in Sweden.
Vornik told Metro the activity is most likely part of Russia’s ‘grey zone’ in the UK and Europe, also including freight parcel bombs, spy rings and the sabotage of deep-sea cables.
His comments are significant as DroneShield has systems in Poland next to the border with Ukraine, which pick up data about UAS launched by Vladimir Putin’s forces.