Several people, including police officers, were injured during the clashes in Sofia.
Anti-vaccine protesters have clashed with police in Bulgaria as they tried to storm the parliament building.
The violence erupted at a protest rally on Wednesday organised by a nationalist group that is fiercely opposing the Bulgarian government’s anti-virus measures.
A heavy police presence prevented protesters from entering the building in Sofia and a number of people were detained. Several others, including police officers, were injured during the clashes before the building was cordoned off.
Nearly 1,000 protesters, waving national flags and singing patriotic songs, remained at the square in front of the National Assembly.
Demonstrators said they planned to stay there until their demands for abolishing the mandatory face masks and vaccination passes are met.
“The aim of the protest is to remove the restrictive measures and especially, first of all, the unconstitutional green certificate,” Kostadin Kostadinov, leader of the Vazrazhdane party, said ahead of the protest.
The nationalist group, which holds 13 seats in Parliament’s 240-seat chamber, has won support among opponents of coronavirus restrictions.
Bulgaria, which is facing a new surge in infections, has vaccinated only a third of its population against COVID-19 -- the lowest rate in the European Union.
Prime Minister Kiril Petkov has called for calm and invited representatives of the protest to his office on Friday to discuss their demands.