Two people were being treated in hospital in the Dutch city of Rotterdam on Saturday after they were seriously injured when the 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 canons.

Rotterdam police said on Twitter on 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”.