Two people were being treated in hospital in the Dutch city of Rotterdam on Saturday after they were seriously injured when police fired shots during a violent protest against COVID-19 measures, authorities said.
Crowds of several hundred rioters torched cars, set off fireworks and threw rocks at police during the protests on Friday evening. Police responded with warning shots and water cannons.
Rotterdam police said on Twitter Saturday that 51 people had been arrested, half of whom were under 18.
"Two rioters where wounded when they were hit by bullets, they remain in hospital," police added.
The city's mayor, Ahmed Aboutaleb, said protest had turned into "an orgy of violence".
"Police were forced to draw their weapons and even fire direct shots," he told a press conference early on Saturday.
Dutch justice minister Ferd Grapperhaus said in a statement that the "extreme violence" against police and fire fighters in Rotterdam was "repulsive".
"The right to protest is very important in our society but what we saw last night was simply criminal behaviour," Grapperhaus said.
Protesters had gathered to voice opposition to government plans to restrict access to indoor venues to people who have a "corona pass", showing they have been vaccinated or have already recovered from an infection, reports Reuters.
The pass is also available to people who have not been vaccinated, but have proof of a negative test.
Organisers of a planned protest Saturday in Amsterdam against the coronavirus measures said they had cancelled the event after Friday's violence.
Even so, several hundred protesters showed up in the city's central Dam square, monitored by a heavy police presence.
In the southern city of Breda, a musical protest called by local DJs against current COVID-19 measures, which include the 8 p.m. closure of bars, restaurants and clubs, attracted a few hundred people. The Netherlands re-imposed some lockdown measures last weekend for an initial three weeks in an effort to slow a resurgence of coronavirus contagion, but daily infections have remained at their highest levels since the start of the pandemic.