Some of the 100,000 marchers attending the demonstration against austerity set fire to cars and throw stones at police

About 100,000 workers marched across Brussels on Thursday to protest against government free-market reforms and austerity measures, and the demonstration ended in violence when people set fire to cars and threw cobblestones and police responded with tear gas and water cannons.

About 50 people were injured and 30 detained, police said, in one of biggest postwar labour demonstrations in Belgium, a country long vaunted as a shining example of an efficient welfare state.

The violence overshadowed a raucous but largely peaceful march for better protection of workers during the economic crisis. The workers were angry at government policies that will raise the pension age, freeze wages and cut into public services.

“They are hitting the workers, the unemployed. They are not looking for money where it is, I mean, people with a lot of money,” said Philippe Dubois, who came from the industrial rust belt of Liege.

Facebook Twitter Pinterest Around 50 people were injured and 30 arrested during the unrest, police said. Photograph: John Thys/AFP/Getty Images

The unexpectedly large march opens a month-long campaign by the trade unions against the business-friendly governing coalition, which will end with a nationwide strike on 15 December.

Despite the opening of talks between the government and employers and unions later on Thursday, socialist trade union leader Rudy df Leeuw vowed to see the protests through to completion.

Belgium has a long postwar tradition of collective bargaining between employers and workers, and successive coalition governments representing the full range of public opinion have often been able to contain social disagreements. But the current coalition, made up of three pro-business parties and the centrist Christian Democrats, is the first in decades that has been able to set such a clear free-market agenda.

The government says it has been forced to push through stringent austerity measures to keep the budget deficit within European Union constraints and insists that businesses need more lenient tax policies to become more competitive in the global market. The trade unions object to government policies that promise to raise the pension age from 65 to 67, freeze the automatic link between wages and inflation, and cut public services in a way that would affect the entire population.