The dpa news agency reported Friday that the Rock am Ring festival was cleared out on its opening night after Koblenz police said they had received information of a "concrete threat".
It draws tens of thousands of people annually. "Intensive investigations are now being carried out", police in the city of Koblenz said on Friday evening, adding that they could give no further details.
Organisers said they hoped the festival would resume on Saturday. We ask all festival visitors to leave the festival in a calm and controlled manner towards the exits and camping grounds.
Rock am Ring has not shared the exact specifications of the terror threat, but it's serious enough to evacuate the festival grounds and surrounding campsites.
Others initially sat down and tried not to move, according to reports on Twitter.
The festival had returned to the Nuerburgring this year after two years at the nearby Mendig airbase, which were marred by lightning strikes on festival-goers.
Police quickly cordoned off the concert venue that was held on a racetrack while helicopters hovered overhead.
Rock am Ring takes place annually in Nuerburg, Germany. "Safety first. See you soon LGx".