The demonstration was organised by the ABVV socialist trade union and the Christian ACV, the country's two biggest unions, with protesters marching from Brussels Central station to Brussels South.
As thousands gathered at the station, a smaller group clashed with police, throwing wooden beams, glass bottles and rubbish bins, The Belgian Times reported. Police were deployed in large numbers around the stations, checking groups of young people not wearing trade union colours.
Police said the main trade union rally went ahead peacefully but "groups of troublemakers were responsible for serious incidents before and after the march." They added that those who "cause the problems of public order are not linked" to the rally.
Reporting from Brussels, Al Jazeera's Rosie Birchard said damage was caused during Friday morning's protests, with an "acrid smell of burning in the air" due to fires and tear gas. "Police [and] emergency services have been arriving, starting to disperse or clean up and then the protests flare up again. So the day is still early; often these things get worse in the evening in terms of the street violence," she said.
Birchard said some young people told her they were inspired by school protests in France and wanted to talk about the education environment they were learning in, adding that the students felt they were "not being listened to".
The clashes followed a week of tension in Liege, where authorities banned gatherings as students clashed with police and vandalised shops. More than 200 people were arrested in Liege and dozens of police were injured.