Seven people were injured in Rotterdam at a rally against stricter anti-coronavirus rules after police fired shots.
"There are casualties in connection with the shots fired," police in the Dutch port city said late Friday. Police later said officers had also been injured.
Police said officers fired initial warning shots and further shots, and that in the case of one person seen shot down in pictures, it was not yet clear how and by whom they were injured.
Dozens were arrested in the rioting.
There were incidents of arson, fireworks were set off and police and firefighters were pelted with objects during the protest against tightened coronavirus measures which saw hundreds of people take to the streets.
Polices said a large force of officers from all over the country were sent out to try to restore order. Riot police and water cannon were also deployed.
As reported by broadcaster NOS, at least one police car was set on fire and others were damaged. Firefighters and police officers were pelted with objects.
Images broadcast showed a patrol car ablaze, fires on the pavement, chairs tossed around and rubbish containers pushed into the street.
Politicians in shock
Dutch politicians expressed shock on Twitter at the extent of the violence.
The city mayor issued an emergency decree to ban people staying at the scene of the riot, the central station and one other station.
Train services to and from Rotterdam were suspended because of the riots, Dutch Railways announced. Service resumed in the early hours of Saturday morning.
The rally, called by several organizations, was against government plans to introduce a regulation requiring proof of virus status in light of the worsening coronavirus situation. Only the vaccinated and those who have recovered would then be allowed access to events, cafes and restaurants.
After a curfew was imposed in the Netherlands in January, there had already been serious riots in several cities, causing millions of euros in damage.