French police again clashed with protesters Saturday as campaigners sought to stop the construction of reservoirs in the southwest, the latest in a series of violent standoffs as social tensions erupt nationwide.

The violent scenes in Sainte-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 UK.

The protest movement against the pension reform have turned into the biggest domestic crisis of Macron's second mandate, with daily clashes in the streets of Paris and other cities between police and protesters.

Several protesters and members of security forces were wounded in the clashes around Saite-Soline as campaigners sought to stop the construction of reservoirs for the agricultural industry, according to the authorities.

A long procession set off late morning, comprising at least 6,000 people according to local authorities and around 25,000 according to the organisers.

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, AFP correspondents said.

Multiple projectiles and improvised explosives were thrown by protesters, with police responding with tear gas and water cannon.

Two protesters were seriously wounded, including one who was hospitalised with a brain injury, the authorities said.

Sixteen members of the security forces were wounded, six of whom were hospitalised regionally and one of whose injuries were so serious he was evacuated by helicopter.

"While the country is rising up to defend pensions, we will simultaneously stand up to defend water," said the organisers gathering under the banner of "Bassines non merci" ("No to reservoirs, thank you").

Eleven people were detained after police seized cold weapons, including petanque balls and meat knives, as well as explosives.