There were outbreaks of violence during protests against coronavirus measures in Brussels on Sunday that drew some 35,000 protesters.
Police car windows were broken, barricades set on fire and people threw fireworks, according to images shown by Belga news agency.
Fireworks and other items were thrown at police and fights broke out with the security forces, according to videos shared on Twitter that claimed to show the protests.
The police said they repelled protesters with water cannon and tear gas. They said 44 people were arrested, in a statement in the evening.
Three police officers were injured and six police vehicles were damaged, and one officer's scooter set on fire.
Shop windows were also damaged, as were cars parked nearby.
The demonstrators were protesting about rules requiring people to show vaccine certificates in more settings, for example to eat at a restaurant.
The demonstration was authorized by the city of Brussels, a spokesperson for the police told Belga. A march route ending at the Belgian capital's European quarter was planned in consultation with the police, she said.
The number of daily recorded coronavirus cases in Belgium has increased significantly in recent weeks, most recently reaching an average of over 12,000 new infections per day in the country of about 11.5 million.
Last Monday, over 20,000 new cases were recorded in a single day.
Between November 13 and 19 there was an average of 268.3 coronavirus-related hospital admissions per day according to official figures, an increase of 29% on the previous week.