Paris CNN  — 

Clashes erupted in Paris on Monday marking May 1, a traditional day of union-led marches, in the wake of hugely unpopular changes to France’s pension system that were signed into law last month.

A building caught fire at Place de la Nation as the French capital turned into a pitched battle between protesters and riot police.

Around 112,000 people took part in Monday’s protest in the French capital, said Paris Police. It is the second-highest turnout since demonstrations against pension reform began this year, according to CNN affiliate BFMTV.

A CNN team on the ground reported chaotic scenes from the protests, having witnessed fireworks and other projectiles thrown at the police who answered with tear gas as they retreated and regrouped.

The building that caught fire at Place de la Nation, the end point of the protest, was contained. Police said two fuel containers in front of a work site were set on fire by a radical fringe, which was later put out.

Tear gas choked the air in Place de la Nation as clashes continued and protesters showed no sign of dispersing later on Monday.