Rock am Ring, one of the biggest music festivals in Germany, was abruptly shut down on Friday evening due to a terror warning. Festival organizers said on Facebook that police told them to interrupt the festival and vacate the premises as an act of precaution.

Festivalgoers were advised to leave the grounds in a “calm and controlled manner.” Local police said in a statement that the decision to cancel the festival was made due to “concrete leads” for a terror threat.

“As safety is paramount, and it is necessary to exclude a threat to festival visitors in any case as far as possible, it was decided to suspend the festival for this day,” police said.

“After a threat could not be ruled out, all necessary measures were taken immediately. This led to the event being interrupted today for security reasons,” they added.

Almost 90,000 people are estimated to have traveled to the Nürburgring race track near Mendig in western Germany to attend the annual festival, which was scheduled to run until Sunday. In the wake of the terror attack in Manchester, police had already increased security for the festival, with more than 1,200 police officers in the field. According to Sky News, concertgoers left the site calmly while singing “You’ll Never Walk Alone.”

German hard rock group Rammstein were set to perform on Friday night. Die Toten Hosen, System of a Down, the Beatsteaks, Five Finger Death Punch, Frank Carter & The Rattlesnakes, Suicide Silence, and Slaves are among the other acts.

Organizers said that they’d hope to continue the festival on Saturday.