Minor scuffles broke out in the city's downtown between officers and demonstrators, some of whom played drums and horns while chanting against cuts to social welfare programs.
Authorities were also seen escorting some people onto buses before the escalation.
Organizers estimated more than 150,000 were in attendance while the police put the crowd at 80,000.
Belgium’s three major trade unions organized the protest as well as nationwide strikes against cuts to the pension and healthcare systems proposed by Prime Minister Bart De Wever.
He has vowed to slash spending to try and overcome Belgium's economic challenges.
