Police fired tear gas to push back black-clad anarchists who ransacked business premises in the French capital Paris on Sunday during May Day protests against the policies of newly re-elected President Emmanuel Macron.
Thousands of people joined May Day marches across France in which they called for salary increases and for Macron to drop his plan to raise the retirement age.
Most were peaceful but violence broke out in Paris, where police had made 29 arrests so far, Interior Minister Gerald Darmanin said on Twitter.
Clashes with police broke out at the start of the march near La Republique Square and when it reached La Nation Square in eastern Paris.
"Black Bloc" anarchists ransacked a McDonald's restaurant on the Place Leon Blum and trashed several real estate agencies, breaking their windows and setting garbage bins on fire.
Police said activists had even attacked firemen, trying to put out fires. Police responded by firing tear gas.
About 250 rallies were organized in Paris and other cities including Lille, Nantes, Toulouse and Marseille. In the capital, trade unionists were joined by political figures - mostly from the left - and climate activists.
The cost of living was the main theme in the presidential election campaign and looks set to be equally prominent ahead of June legislative elections that Macron's party and its allies must win if he is to be able to implement his pro-business policies, including increasing retirement age to 65 for 62
Joshua Antunes, a 19-year-old student said: "It is important to show Macron and the whole political world that we are prepared to defend our social rights." He also criticized the president's "inactivity" on environment issues.
Marchers carried banners reading "Retirement Before Arthritis", "Retirement at 60, Freeze Prices" and "Macron, Get Out"
"The government has got to deal with the purchasing power problem by raising wages," Philippe Martinez, the head of the hardline CGT union, told Reuters before the rallies.
Macron won a new five-year presidential term after beating far-right challenger Marine Le Pen in last Sunday's runoff vote.
Far-left leader Jean-Luc Melenchon, who came third in the first round of the presidential vote, was attended the Paris march.
He wants to rally a union of the left, including the Greens, to dominate parliament and force Macron into an awkward "cohabitation" but so far this has not materialized.
"We will not make a single concession on pensions," Melenchon said before the march started.
He said he still hoped an agreement to build a new union of the left could be reached by this evening.
Unlike in previous years, Marine Le Pen did not lay a wreath in Paris at the statue of Joan or Arc, whom her party uses as a nationalist symbol. She was replaced by the Rassemblement National Interim President Jordan Bardella, who said Le Pen was preparing for the legislative elections.
Le Pen urged voters in a video message to elect as many deputies from her party as possible in June so that she could "protect your purchasing power," and prevent Macron from carrying a "harmful project for France and the French people."
The parliamentary elections will be held on June 12 and 19.