The incident comes amid jitters about possible infrastructure vulnerability to potential Russian sabotage.
Security at a NATO airbase in western Germany has been raised because of intelligence information pointing to a “potential threat.”
All staff not essential to missions have been sent home as a precaution.
The Geilenkirchen air base, near the border with the Netherlands, is where the alliance’s Airborne Warning and Control System (AWACS) aircraft are based.
A NATO post on X, formerly known as Twitter, late on Thursday did not elaborate on the nature of the potential threat. It said that “operations continue as planned.”
German police confirmed the deployment of vehicles to the scene on Thursday night but gave no details.
Last week, a major German air force based near Cologne was locked down for several hours amid fears that its water supply might have been tampered with.
An investigation found no evidence of such sabotage. There were also reports of suspicious observations at Geilenkirchen and a person was briefly detained for questioning near the base.
On Thursday, prosecutors in Flensburg, in Germany’s north, said they were investigating suspicions of espionage for sabotage, without elaborating on who might be behind it.
German media also reported that drones had been spotted over a chemical park in Brunsbuettel, on the North Sea coast.