BRUSSELS — Police have arrested dozens of people and deployed tear gas and water cannons against a group of protesters at Boulevard Pachéco during a national strike that could be Belgium’s biggest in a decade.

Several people were injured after the clash with police, with some visibly shaken up and others angry with the authorities.

Belgium’s trade unions are protesting against austerity measures introduced by the right-wing government coalition led by Flemish nationalist Bart De Wever, of the nationalist New Flemish Alliance. At the center of their anger is a pensions reform that would raise the age of retirement from 65 to 67 by 2030.

“We were just marching peacefully and suddenly there were smoke bombs and police. I don’t get it. For maybe 10 troublemakers … they tear-gassed the entire crowd, the elderly, the children … It was shameful, an absolute disgrace,” said Rafael, a postal worker, whose eyes were red from the gas.

“Instead of addressing the issue, we prefer to tear-gas the entire population exercising its right to strike,” said another participant, who didn’t want to share his name.

Masked protest participants vandalized the Immigration Office building on Pachéco, with the entire incident filmed by Anneleen Van Bossuyt, Belgium’s migration minister.

“The vandalism against my services has nothing to do with the right to strike. Anyone who attacks our employees or our buildings is attacking our society. My support goes out to the staff who have to endure this. Despite the massive efforts of the police, these thugs have shown their true face,” she wrote in a post on X.

Further incidents took places in other parts of Brussels, including at a Hilton hotel opposite the Central Train Station, where protesters who threw projectiles and glass bottles faced off with police, who responded with water cannons and tear gas. The offices of political parties Vooruit and the Socialist Party were covered in graffiti.

Police have estimated that around 80,000 people came out to protest, while Thierry Bodson, head of the socialist trade union FGTB-ABVV, said as many as 140,000 were taking part. A one-day general strike in 2014 saw 100,000 people take to the streets.

This story is being updated.