Protesters danced on the top of overturned cars and threw paving stones and fireworks during the protest, which opposes economic reforms announced by Prime Minister Charles Michel's centre-right coalition. Riot police armed with clubs and shields charged the rowdiest groups of demonstrators, who also set rubbish bins on fire and made makeshift barricades, AFP journalists witnessed.
Paramedics treated at least one protester, who suffered a broken nose. The rally is the first in a series of measures planned by Belgian trade unions including strikes in several provinces in coming weeks, followed by a general strike throughout the kingdom on December 15.
Police said there were at least 100,000 demonstrators in Brussels while the unions said up to 130,000 protesters showed up. Rail companies had sold low-cost tickets to increase protest numbers in the capital.
Public transport services were restricted because of the protests, partially paralysing the capital of the European Union on a day that finance ministers from countries that use the euro were gathering there. Member states like Greece, Spain and Italy have also experienced violent protests against austerity.
The cabinet planned to hold a crisis meeting with the three main unions today. The Brussels rally as a whole was peaceful, bright and noisy as crowds of people wearing union reds, blues and greens marched through the boulevards, holding banners, throwing firecrackers and whistling.
Workers and staff at steel firms, the ports of Antwerp and Zeebrugge, the post office and in education were also planning to stage a work slowdown.
"The whole raft of government measures create a potentially explosive cocktail," Marie-Helene Ska, secretary general of the leading Belgian union, CSC, warned earlier in the newspaper Le Soir.