It comes after drones were also spotted recently over airports and military sites in Denmark and Norway, with suspicion falling on Russia -- allegations rejected by Moscow.

Interior Minister Alexander Dobrindt said Germany needed to "find new responses to this hybrid threat", including greater capabilities to detect, assess and potentially shoot down drones.

"Much of what we see today can be viewed as provocation -- and this is also how we assess the incidents we saw last week in Schleswig-Holstein," a northern coastal state, Dobrindt said.

Authorities had already revealed that a swarm of drones had been spotted over the state at the end of last week.

State interior minister Sabine Suetterlin-Waack told lawmakers on Wednesday that "drone-like aircraft were sighted and reported" in several areas, "including over critical infrastructure and military installations".

She did not say who was to blame, and added the threat level in the state had not increased.

According to news magazine Der Spiegel, drones were first spotted hovering over a naval shipyard facility belonging to Thyssenkrupp Marine Systems on Thursday night.

Other facilities apparently scouted by the drones included a coastal power plant, an aviation fuel refinery and the Kiel Canal, according to the report.

The Bild tabloid reported that the drones were believed to have been dispatched from a "foreign-flagged ship" in the Baltic Sea, thought to belong to Russia's so-called "shadow fleet" of sanction-busting vessels.

A large "mother" drone was sent off from the vessel and then released a swarm of smaller drones, it said.

Dobrindt last week announced that Germany is planning to create a new "drone defence centre" that will pool the expertise of Germany's federal and state governments.

He also said he wants to revise air safety laws to allow the "shooting down of drones" by the armed forces.

EU leaders are discussing bolstering Europe's defences at a summit in Copenhagen from Friday.