Police in Paris have used tear gas and water cannon to disperse protesters, in a second weekend of demonstrations sparked by rising fuel prices.
Violence erupted on the Champs-Elysées as protesters tried to get through a security cordon around sensitive sites.
About 5,000 protesters had converged on the avenue. At least 18 people were arrested after clashing with police.
Organisers of the "yellow jacket" movement billed the latest protests as "act two" in their rolling campaign.
Named after their distinctive high-visibility attire, the protesters oppose an increase in fuel duty on diesel.
Demonstrators on the Champs-Elysées came up against metal barriers and a police-enforced perimeter that stopped them reaching key buildings such as the prime minister's official residence.
Some erected barricades, lit fires, ripped up paving stones and threw them at police while shouting slogans calling for President Emmanuel Macron to resign.
Police say 19 people were injured in the clashes.
Interior Minister Christophe Castaner accused protesters of being influenced by the leader of the far-right National Rally party, Marine Le Pen. But she accused him, on Twitter, of dishonesty.
By early evening police were clearing the Champs Elysées but the situation remained tense, with hundreds of protesters holding out.
Demonstrations staged in other cities - including Lille, Lyon and Bordeaux - were largely peaceful.
The interior ministry has put the total number of protesters at 81,000 so far - fewer than the first day of yellow-jacket demonstrations, which drew some 280,000 people a week ago.
Meanwhile a march against sexual violence was kept well away from the unrest over fuel prices in Paris.
Why wear yellow jackets?
All drivers in France have to carry the jackets in their cars as part of safety equipment for use in a breakdown.
Along with the familiar red reflective triangle which must be placed behind a broken-down vehicle on the side of a road, the high-visibility jacket - or "gilet jaune" - must be worn by the driver outside the car.
Failure to wear the jacket after a breakdown or accident can result in a €135 ($225) fine under a law introduced in 2008.
What happened last weekend?
There were protests at more than 2,000 locations across France. Two people were killed and more than 600 injured.
At least 50 people were also arrested, although most of the protests took place without incident.
Several of the injuries and one of the fatalities came when drivers tried to force their way through protesters.
The second death was that of a male demonstrator on a motorbike who collided with a lorry.
Synonymous with driving, the jackets have now morphed into the uniform of the movement against higher fuel costs.