NANTES, Feb 22 (Reuters) - Violence erupted when about 20,000 people demonstrated against an airport project near the city of Nantes on Saturday, 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, with some activists occupying the area by living rough in makeshift wooden cabins.
Police have tried several times in vain to evict the squatters and have had to contain many demonstrations.
The protesters, including farmers, locals and green politicians, argue the new airport will damage the environment and is a waste of public money during an economic crisis.
The protest on Saturday in Nantes, homeland of French Prime Minister Jean-Marc Ayrault, involved around 20,000, according to police, and was the first since local authorities gave the project a green light.
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.
"I regret that this demonstration transformed itself into a genuine urban guerrilla, escaping the organisers' control," French Interior Minister Manuel Valls said.
The 580-million-euro aiport is planned to be finished in 2017. (Reporting by Guillaume Frouin; Writing by Astrid Wendlandt; Editing by Andrew Roche)