Riot police flooded the streets and clashed with protesters in the western cities of Nantes and Rennes.
About 200 demonstrations were expected nationwide.
Police said around 10 people had been arrested in the capital, where demonstrators marched under banners reading "We want better" and "A giant leap forward to the 19th century".
The strike shut the Eiffel Tower, disrupted train services and saw dozens of schools closed or barricaded by students. Public transport in Paris was set to see the most disruptions. Additionally, hospital workers in Paris, postal workers and members of the press and TV were also set to strike.
Last week tens of thousands of angry students and workers took to the streets over what they argued were plans to make it easier for struggling companies to fire workers.
A battle is also taking place within French President Francois Hollande's ruling Socialist party, with many on the left of the party fiercely opposed to the reforms, which some analysts have billed as a last-gasp attempt to boost France's economy before next year's presidential election.
Hollande has vowed not to run again if he cannot put a dent in the country's unemployment figures -- long stuck at around 10 per cent -- and hoped the modest labour reforms would encourage firms to hire more people.
But pressure from the street and parliament's back benches caused the government to water down the proposals so that they only apply to large firms. Despite such watering down, however, a recent poll found that 58 per cent of the French public still opposed the measures.
The protests coincide with strikes by air traffic controllers that was expected to cause travel chaos for thousands of passengers, while drivers faced more than 400 kilometres of tailbacks on motorways around Paris. Charles de Gaulle airport in Paris was not due to see cancellations but airport chiefs warned of delays.
Analysts said the demonstrations were yet another challenge to Hollande's authority, coming a day after he scrapped the constitutional reforms he proposed following the Paris attacks, including a plan to strip convicted terrorists of their French nationality. Hollande said agreement between the two houses of parliament on the measures would be impossible.