Police fired teargas to disperse the crowd, who defied an 11:00 pm coronavirus curfew on Friday and just stayed on into Saturday afternoon in the area around a race course near Redon in Brittany.
There were "very violent clashes" when 400 police intervened, prefect Emmanuel Berthier said, adding the violence lasted more than seven hours through the night.
"The rave party at Redon has ended," he announced after police had cleared the area.
Police detainedfive men and opened an inquiry into violence against people in positions of public authority.
According to the authorities, 11 police officers were injured, two of whom were taken to hospital.
Two of the ravers were also hurt, including a 22-year-old man who lost a hand.
Berthier said the "people had an objective, to confront the forces of public order".
Berthier told AFP that the group threw "Molotov cocktails, metal balls and bits of breeze blocks".
A police officer said it was not usual for people to bring the metal balls used in the French sport of boules or petanque to a rave.
Event organisers said police had chosen violence instead of dialogue by firing tear gas grenades.
"It was war," said Flo, a 22-year-old man who attended the event.
"There hasn't been any music since last night," but "people taking part in the illegal rave are still on the scene," the prefect's office had told AFP early Saturday.
Local authorities had on Friday banned the party, which came two days before the coronavirus curfew is set to be lifted as Covid-19 case numbers fall in France.
The rave had originally been set up in memory of a young man killed in nearby city Nantes two years ago during the annual nationwide Fete de la Musique celebration.
Prosecutors said Friday that Steve Maia Canico fell into the Loire river when police moved in to break up the gathering.
His body was found more than a month later and protesters in Nantes have demanded "Justice for Steve", saying the police intervention was disproportionate.
Hundreds of people flouted France's coronavirus curfew with underground parties near Dijon and a village in western Brittany, while police managed to prevent organisers from staging a major rave in Paris.
