Around 160,000 people joined demonstrations across France Tuesday, the interior ministry said, heeding union calls for President Emmanuel Macron to "maintain the social model" under threat from austerity reforms.
The head of the hard left Confederation of Labour (CGT) union Philippe Martinez estimated turnout nationwide at 300,000 to dub the rallying call a success.
The ministry said 16 arrests were made, nine in Paris, where one marcher and a policeman were reported hurt after up to 300 hooded anarchists latched onto the rally, throwing projectiles at police, who responded with teargas.
Around 20,000 people turned out in Paris, the largest of some 100 rallies across the country.
Marchers -- mainly young people, some of them school age -- carried banners saying they had had enough of "austerity, unemployment", while the elderly also turned out to voice their disapproval of pensions policy.
"I've lost 50 euros a month -- I can't make ends meet any more," complained Francois Manugal, a retired 65-year-old from the southeastern city of Lyon.
Martinez criticised Macron's attempts to reform the economy, in particular "questions of wages," accusing the government of believing that "reducing social contributions would be good for purchasing power."
Pascal Pavageau, the leader of the Force Ouvriere union, urged the government to engage in "dialogue and above all maintain the social model," as Macron battles sagging popularity on the back of sweeping reforms notably of the labour code designed to bring greater flexibility to the jobs market.