Authorities ordered the more than 10,000 people gathered at the track in the western city of N?rburg evacuated pending an inspection of the site, Efe reported.
Festival organisers agreed to cancel Friday's performances after police issued the alert roughly six hours after the start of the three-day event.
Police said the alert was based on "concrete indications" that made it impossible to exclude "a possible terrorist threat."
The government of Rhineland-Palatinate state confirmed that an alert was in effect, but did not provide any further details. Police established a telephone number for festival-goers seeking information.
Launched in 1985, Rock am Ring takes place annually at the N?rburgring and some 85,000 people were expected to attend this year's edition.
(This story has not been edited by Social News XYZ staff and is auto-generated from a syndicated feed.)
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Doraiah Chowdary Vundavally is a Software engineer at VTech . He is the news editor of SocialNews.XYZ and Freelance writer-contributes Telugu and English Columns on Films, Politics, and Gossips. He is the primary contributor for South Cinema Section of SocialNews.XYZ. His mission is to help to develop SocialNews.XYZ into a News website that has no bias or judgement towards any.