Police have fired water cannon and tear gas at stone-throwing protesters after tens of thousands of demonstrators marched through Brussels against Covid-19 rules.

Authorities estimated that around 50,000 people paraded through the Belgian capital on Sunday — the largest in a spate of protests in the city over the past months.

Clashes broke out close to the headquarters of the European Union as police used water cannon and tear gas to push back protesters hurling paving stones and firecrackers.

Although Belgium announced a slight easing of restrictions on Friday, the government also said people must have booster shots after five months to maintain the Covid-19 passes which allow them to access bars or cinemas.

The passes, which are mandatory for anyone wishing to enter a restaurant, museum or many other public space, have sparked fierce opposition among some Belgians.

Protesters carried signs slamming Belgium Prime Minister Alexander De Croo and the Covid Safe pass required for entry into numerous venues.

READ MORE:Thousands protest in Europe against vaccine passports, strict Covid rules

'Health dictatorship'

Organisers including the World Wide Demonstration for Freedom and Europeans United for Freedom had called for people to come from other EU states.

Flags from Poland, the Netherlands, France and Romania could be seen in the crowd.

The protest comes as the Omicron wave causes infections to reach record highs across Europe.

"What has been happening since 2020 has allowed people to wake up to corruption," said Francesca Fanara, who had travelled from Lille in northern France.

"It's a health dictatorship," said Adolfo Barbosa from Portugal.

Belgium is in the midst of a fifth wave of Covid-19 infections, with the peak not expected for at least a couple of weeks.

The daily infections surge was over 60,000 in the past week in what authorities have called a "tsunami".

READ MORE: Covid-19 curbs, mandates spark protests across Europe