Police have used water cannons and tear gas on several hundred hooded youths who joined a protest march in Paris against French President Emmanuel Macron’s pro-business labour policies.
The youths who showed up near the end of the march pelted security forces with objects, briefly halting the event held by unions and other groups.
While union marches are usually peaceful, troublemakers on the margins often clash with police.
The CGT union, which organised marches around France, said 60,000 people participated in the Paris protest.
Police put the figure at 24,000. A statement said four people were detained and one person with a minor injury was taken to hospital.
The protests are the first big public display of discontent with Mr Macron’s presidency, which kicked off in May amid enthusiasm over his promises of revving up the French economy but is now foundering amid anger over the labour decrees and other domestic troubles.
Thousands of union activists marched on Tuesday morning in the Mediterranean city of Marseille, in Le Havre on the English Channel and other cities.
The CGT union had called for strikes and organised 180 marches against labour decrees unveiled last month by Mr Macron’s government.
The Eiffel Tower was affected by the union-organised protests, with afternoon viewing limited to the first floor, which visitors had to access by a stairway.
Horn-tooting funfair workers held a separate protest against legal changes they say favour big corporations and could wipe out their centuries-old industry.
Dozens of big rigs drove at a snail’s pace around the Arc de Triomphe, causing rush-hour traffic jams as protesters danced and waved flags on a flat-bed truck with a severed plastic head from a funfair ride.
The workers said they timed their protest to coincide with the broader labour demonstrations, since both movements are about workers fearing their jobs are at threat.
"Everybody likes funfairs. Everybody has been to a funfair one time in his life," bumper car worker Sam Frechon said. "Funfair is France."
Meanwhile, thousands of union activists marched in the Mediterranean city of Marseille, in Le Havre on the English Channel and other cities.