People hurled fireworks at police and set fire to bicycles in The Hague, one night after protests in Rotterdam turned violent and police opened fire.
Thousands of demonstrators also took to the streets in Austria, Croatia and Italy as anger mounted over new curbs.
Its regional director Dr Hans Kluge told the BBC that unless measures were tightened across Europe, half a million more deaths could be recorded by next spring.
“Covid-19 has become once again the number one cause of mortality in our region,” he told the BBC, adding “we know what needs to be done” in order to fight the virus – such as getting vaccinated, wearing masks, and using Covid passes.
Many governments across the continent are bringing in new restrictions in a bid to tackle rising infections. A number of countries have recently reported record-high daily case numbers.
At least three demonstrators are receiving hospital treatment for gunshot wounds, officers said. Authorities have launched an investigation into the incident.
The Netherlands imposed a three-week partial lockdown last Saturday after recording a record spike in Covid cases. Bars and restaurants must close at 20:00, and crowds are banned at sports events.