German authorities shut down and cleared thousands of fans from a popular rock music festival Friday night after receiving a "concrete" terrorist threat.

Rhineland-Palatinate government spokesman Joachim Winkler told the dpa news agency that there were tips of a possible terrorist attack and that the Rock am Ring festival was shut down on its opening night as a precaution.

The German band Rammstein was the Friday night headliner, but hadn't yet started playing.

Organizer Marek Lieberberg told journalists at the scene that he hoped the annual three-day festival would be able to resume Saturday as planned, but that it was not yet clear.

The festival grounds were clear by 9:30 p.m., about a half hour after people were told that they were going to have to leave.

"The public reacted fantastically," Lieberberg said.

It wasn't immediately clear how many fans were in attendance, but some 90,000 were expected by the end of the weekend at the event outside the western town of Nuerburg. Overall, some 85 bands were scheduled to play on four stages with Germany's Toten Hosen highlighting Saturday's list and California's System of a Down playing Sunday.

Following the recent attack in Manchester outside a concert, organizers had instituted strict security controls including body searches, while backpacks and bags were banned. Some 1,200 police were to be on hand for the event, in uniform and in plain clothes.

Germany has been on alert since a number of violent attacks last year, including the truck attack on a Berlin Christmas market that left 12 victims dead and dozens of others injured. The attack, carried out by a young Tunisian man who had been denied asylum in Germany, was claimed by the Islamic State group.