Fans hoping to see German rock giants Rammstein streamed out of the Nuerburg arena after organisers asked them to leave in a "calm and controlled" way.
"Due to a terrorist threat the police have advised us to interrupt the festival," they said.
A bomb at a concert in Manchester claimed 22 lives last month.
Some 85,000 people were expected to visit the three-day festival, Efe news agency reports. It falls on the Pentecost holiday weekend.