Fifteen protesters were arrested in Paris, where two policemen were injured, and another 19 students were detained in the western city of Nantes.
The reforms, which had been significantly watered down under pressure from an earlier wave of protests, were adopted yesterday by the cabinet of the increasingly unpopular President Francois Hollande, who hopes to stand for re-election next year.
"Young and insurgent, the world is ours" read one banner as some 5,000 students yesterday protested in the French capital, where students torched two cars, threw bottles at riot police and emptied a rubbish bin over other officers.
Video of a policeman punching a student went viral on social media, and an enquiry has been opened into the incident.
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Protests were staged in dozens of other cities, including Marseille, Bordeaux, Toulouse and Lyon with a total turnout estimated at 43,000.
Students have been at the forefront of protests over the reforms aimed at freeing up the job market and reining in France's 10 per cent unemployment rate.
Among youths, joblessness is nearer to 25 per cent -- among the highest in Europe.
Many young people, including graduates, find themselves working on short-term contracts for several years after their studies, or doing internship after internship while hoping to secure a job.
One of yesterday's protesters in Paris was dressed as a capitalist, wearing a top hat and smoking a cigar with a sign reading "Business, power, finance -- all together!"
Around 58 per cent of the French people oppose the measures, according to a recent poll.
Prime Minister Manuel Valls has touted the reforms as "intelligent, audacious and necessary" in the face of stubbornly high unemployment, which has not dropped below seven percent in 30 years.
"Our country has become used to (joblessness) for too long," he said.