Thousands of people gathered at an unauthorized rave near Bourges, France, where techno music played across a former military firing range.

Attendance grew from an estimated 20,000 to as many as 40,000 by Saturday evening.

Authorities raised safety concerns after bomb disposal experts removed an unexploded shell from the site.

Officials warned the area may still contain dangerous World War II-era ordnance, France 24 has reported.

The event comes as France considers stricter laws against illegal rave parties, including fines for attendees and prison sentences for organizers.