The rave party in central France began on Friday in Cornusse and will continue all weekend, according to the organizers.
The regional government is issuing sharp warnings, saying the site "is extremely dangerous as explosive ordnance may be present there," according to Philippe Le Moing Surzur, head of the department.
Modern ammunition poses no danger, he said, but old ammunition can detonate.
"The place has been used for 150 years, and we know that there may be ammunition in the area," Le Moing Surzur said, appealing to dancers to avoid forest areas where the risk of hidden duds is higher.
