Protesters threw rocks and fireworks at them and set police cars ablaze.
Hundreds of protesters had gathered to show their anger at government plans for a Covid vaccine pass, and a ban on fireworks on New Year’s Eve.
The Netherlands imposed a three-week partial Covid lockdown last week as cases surged.
Seven people were injured in total and at least 20 arrested in a night condemned by Rotterdam’s mayor as “an orgy of violence”.
Police fired warning shots and direct shots “because the situation was life-threatening”, a police spokesperson told Reuters news agency.
The city was placed under a state of emergency and its main train station closed as a result of the violence.