In Belgrade, riot police deployed tear gas to disperse crowds after protesters threw water bottles during an attempted arrest.
Thousands gathered in other cities, including Novi Sad, where supporters of the ruling Serbian Progressive Party threw flares and firecrackers at protesters, who smashed office windows in response.
The protests, led mainly by students, demand early parliamentary elections and the resignation of Interior Minister Ivica Dačić over recent violence at demonstrations.
Police said dozens were injured nationwide, including 16 officers, following incidents in Vrbas, Bačka Palanka and other towns.
