The protesters began setting up barricades in Brussels after the police used tear gas to disperse the demonstrators on Sunday, a Sputnik correspondent reported from the scene.
The participants of the rally were protesting against newly imposed restrictions, such as banning the unvaccinated from visiting bars, restaurants, cinemas, and gyms.
The event attracted some 35,000 people and led to gridlocks in the streets and tunnels in the city centre, according to the police.
According to the AFP, the demonstration, dubbed "Together for Freedom", was initially peaceful, but a group of protesters began pelting projectiles at the police, prompting law enforcement officers to respond with water cannons and tear gas.
The Belgian government rolled out the new measures to tackle the spread of COVID on Wednesday. Apart from making COVID certificates mandatory to visit a range of public venues, the authorities ordered everyone older than 10 to wear masks in all public spaces except schools, and urged the employees to work remotely at least four days a week.
Mass demonstrations have hit European capitals in recent weeks as governments have imposed new anti-COVID measures to curb the rapidly growing number of new infections. Rallies in the Netherlands resulted in riots on Saturday, with police arresting some 30 people.