The march was held to protest against the arrest of a woman for “rebellion” in the city on Monday who has since accused the police of racism, a police spokeswoman said.
The police have rejected that charge, claiming that the woman had resisted arrest.
The spokeswoman said that on Saturday “young people joined the group of peaceful protesters and then left the demonstration to go and wreck the city centre”.
They “threw stones at the central police station and police vehicles,” she told AFP.
An officer on a motorcycle who was knocked to the ground and assaulted has been hospitalised, while several other officers were also wounded, she added.
“We are dealing with two hundred young people, ‘casseurs’, who move very quickly, in groups, and loot stores.”
“Casseurs” is a French term which translates as “breakers” and describes black-clad protesters who infiltrate protests to smash property and provoke clashes with police.
“They ransacked a whole McDonald’s,” said the spokeswoman in the city in Belgium’s French-speaking Wallonia region.
Police reinforcements were being deployed to deal with the trouble and by late Saturday the city centre calm had been restored.
The police urged citizens not to go to the city centre, and the mayor had told shops in the affected area to close.