2,500 revelers attended an illegal New Year's Eve party in northwestern France , sparking violent clashes with police, who were unable to stop them and sowing concern over the spread of the coronavirus, authorities reported Friday.

The revelers had organized the clandestine event in Lieuron, south of Rennes, in the Brittany department, after skirmishes with police, a statement from the local prefecture said. Many were still at the scene Friday when a sanitary cordon was installed around them.

Local gendarmes tried "to prevent this event, but faced fierce hostility from many partygoers" who set fire to one of their vehicles and threw bottles and stones,