For a third weekend, French riot police clashed with “yellow vest” protesters in the heart of Paris, posing one of the largest and most sustained challenges Emmanuel Macron has faced in his 18-month-old presidency.
The police fired tear gas, stun grenades and water cannon on Saturday at crowds trying to breach security cordons on the Champs-Élysées ahead of a third rally against high fuel prices.
The authorities said 24 people had been arrested amid concerns that violent far-right and far-left groups were infiltrating the “yellow vests” movement, a spontaneous, apparently leaderless grass-roots rebellion against diesel tax increases and the high cost of living.
“We’re worried that small groups of rioters that aren’t yellow vests will infiltrate to fight security forces and challenge the authority of the state,” said Denis Jacob, secretary general of the Alternative Police union.
“Given the high level of security around the Champs, the fear is thugs will go to other places.”
For two weeks, the “gilets jaunes” or yellow vests, who take their name from the high-visibility jackets all drivers in France must carry in their vehicles, have blocked roads in protests across France.
Thousands of protesters, who have largely organized themselves online, converged on Paris, turning the Champs-Élysées into a battle zone as they clashed with the police firing tear gas and water cannons.
Two people were killed and hundreds of protesters and police were injured on Nov. 17, when the protests kicked off.
Last week, the French authorities said 8,000 people demonstrated on the famed avenue. Some of the protesters set fire to barriers and plywood boards, and the police fired tear gas and water cannons to push back angry demonstrators.
Several hundred yellow vests converged under the Arc de Triomphe at the top of the Champs-Élysées on Saturday and sat down to sing “La Marseillaise,” the national anthem, and chant “Macron Resign!”
“There’s a lot of incitement on social media, and we are expecting excess and violence,” David Michaux of the U.N.S.A. police union told Reuters, adding that far-right and far-left groups were expected.
Three formal demonstrations were planned across Paris on Saturday, including the yellow vests, a union protest against unemployment and a separate rally against racism.
Officials said they expected some 5,000 police and gendarmes in Paris on Saturday, up from about 3,000 on Nov. 17. Another 5,000 will be deployed across France for other yellow vests protests.
Work crews erected metal barriers and plywood boards on the glass-fronted facades of restaurants and boutiques lining the Champs-Élysées. It will be closed to traffic, with pedestrians funneled through checkpoints.
All subway stations in and around the avenue were closed for security reasons, the Paris public transport operator RATP said.
For now, the yellow vests enjoy widespread public support. When they began, the protests caught Mr. Macron off guard just as he was trying to counter a plunge in popularity, with his approval rating at barely 20 percent.
His unyielding response has exposed him to charges of being out of touch with ordinary people. Mr. Macron had planned to meet with members of the yellow vests on Saturday, but those plans were apparently canceled when few representatives showed up.
The protests in France even inspired rallies in Belgium, where on Friday hundreds took to the streets, stopping cars and blocking roads as they called for their own prime minister, Charles Michel, to resign.
On Sunday, about 25,000 people, including yellow vests, plan to protest in Brussels against inaction on climate change. To accommodate the expected throngs, the city’s subway services will be free.