THE HAGUE—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. Police fired warning shots and water cannons at crowds of several hundred protesters who torched cars, set off fireworks, and threw rocks at police during the protests on Friday evening. 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 condemned  “extreme violence” against police and firefighters in Rotterdam as “repulsive.” “The right …