Police and protesters have been hurt in riots that broke out outside the National Assembly in the Serbian capital Belgrade.
The protests began peacefully on Tuesday evening and included students and families, angered by a decision to re-impose a weekend curfew because of a rise in coronavirus infections.
Protesters broke into the assembly, prompting police to intervene.
Clashes erupted and police fired tear gas to disperse the protesters.
Far-right nationalists have been blamed for stirring up the unrest and storming the assembly building. Serbian media said they included an MP who has pushed anti-vaccine and anti-5G conspiracy theories.
Why the protests began
On Tuesday, Serbia saw its deadliest day so far in the pandemic. President Vucic announced in a televised address that there had been 13 further deaths and 120 people were on ventilators, with 4,000 people being treated in hospital.
The situation was most alarming in Belgrade, he said, before imposing a ban on gatherings of more than five people from Wednesday, with a curfew in force from 18:00 local time (16:00 GMT) on Friday until 05:00 on Monday morning. For now, the curfew will apply only to the capital, but Mr Vucic is keen for it to be extended nationally.