Violence erupted after 20,000 people demonstrated against an airport project near the city of French city of Nantes, leaving six riot police officers injured.
Environmental activists have been protesting for more than a year against the government's plan to build a new airport for the west of the country. Some activists have occupied the area by living rough in makeshift wooden cabins.
Riot police used tear gas to disperse protesters who lobbed projectiles and threw paint onto Nantes' city hall, set fire to construction vehicles and vandalised the offices of Vinci, the project's contractor.
The 580-million-euro airport is planned to be finished in 2017.