Riot police fired rubber pellets and tear gas at youths who pelted them with stones and torched cars Thursday in the heart of Paris, a violent turn in nationwide protests against a new labor law that brought a quarter-million people onto France’s streets.

Police and rioters waged a back-and-forth battle amid acrid clouds of tear gas outside the Sorbonne University on the Left Bank. Several hundred youths threw firebombs, chunks of pavement, metal crowd-control barriers, and tables and chairs taken from nearby cafes.

In all, police said some 247,000 protesters participated in nearly 200 marches across the country.

Their anger focuses on a new form of job contract that will allow employers to fire young workers within their first two years in a job without giving a reason.