Riot police with batons and shields broke up a crowd of several thousand who had gathered in Amsterdam on Sunday to protest against COVID-19 lockdown measures and vaccinations.

Public gatherings of more than two people are prohibited under restrictions imposed by the Netherlands in an effort to prevent the omicron variant of the coronavirus overwhelming an already strained health care system.

According to the ANP news agency, around 10,000 people had turned out for the afternoon event in front of the capital's Rijksmuseum, despite a ban on large gatherings. Clashes erupted at the national museum site between demonstrators and riot police, with four officers injured when some people in the crowd tried to break through a police barricade.

At least 30 people were detained after scuffles. Among other things, they were accused of disturbing public order, physical abuse or unauthorized possession of weapons.

Video footage showed police using batons against a group of women and men. Several hundred riot police officers had been deployed in advance of the protest.

Amsterdam Mayor Femke Halsema had issued an emergency ordinance, empowering police to clear the central Museum Square, after the protesters defied a ban on public gatherings.

The protesters, who mostly did not wear masks or abide by social distancing rules, ignored an order not to hold a march and walked along a main thoroughfare, playing music and holding yellow umbrellas in a sign of opposition to government measures.

Similar unauthorized gatherings, described by organizers as communal "coffee drinking" events, have descended into rioting in the past.

The Netherlands went into a sudden lockdown on Dec. 19, with the government ordering the closure of all but essential stores, as well as restaurants, hairdressers, gyms, museums and other public places until at least Jan. 14.