Protesters and French security forces clashed over constructing farm reservoirs in the southwest.
The violent scenes in Saite-Soline in western France came after days of violent protests nationwide over President Emmanuel Macron's pension reform that prompted the cancellation of a visit by King Charles III of the U.K.
A long procession set off late morning, comprising at least 6,000 people according to local authorities and around 25,000 according to the organizers.
More than 3,000 members of the security forces were deployed, with "at least 1,000" potentially violent activists, including some from Italy, present, officials said.
Around the construction site, defended by the police, violent clashes quickly broke out between the security forces and radical militants, Agence France-Presse (AFP) correspondents said.
Multiple projectiles and improvised explosives were thrown by protesters, with police responding with tear gas and water cannon.
"While the country is rising to defend pensions, we will simultaneously stand up to defend water," said the organizers gathering under the banner of "Bassines non merci" ("No to reservoirs, thank you").
Eleven people were already detained after police seized cold weapons, including petanque balls, meat knives, and explosives.
The protest against the pension reform has turned into the most extensive domestic crisis of Macron's second mandate, with daily clashes in the streets of Paris and other cities between police and protesters.
