It is Belgium's three largest trade unions that are behind the demonstrations. They are turning against Prime Minister Bart de Wever's proposed austerity measures of the state's expenditures, which he has promised to introduce to address the country's deficit.
Minor scuffles are reported to have broken out between police and demonstrators and the large crowds have in some places stopped traffic.
The organizers claim that 150,000 people are participating, while the police put the figure at 80,000.
