Several thousand people faced off on both sides of the police cordons on Sunday, with officers in full riot gear standing in several rows between the shouting crowds who threw bottles and flares at each other.
Tensions in Belgrade soared a day after tens of thousands of people joined a huge rally in the northern city of Novi Sad that marked the first anniversary of a train station disaster there which killed 16 people, and triggered a youth-led movement demanding political changes, which has challenged Vucic's firm grip on power.
Anti-government protesters in Belgrade gathered in support of Dijana Hrka, the mother of Stefan Hrka, one of the Novi Sad station tragedy victims.
Hrka said she was launching a hunger strike near a tent camp outside the parliament building which has been occupied by Vucic's loyalists since March.
Protesters on Sunday evening also gathered in Novi Sad and some smaller towns in support of Hrka.
The commemoration rally on Saturday in Novi Sad also reflected major discontent with Vucic's 13-year-long increasingly authoritarian rule.
Youth-led protesters are demanding an early election they hope would oust the populist government from power.
Protesters believe that rampant government corruption and nepotism during renovation work on the Novi Sad station building led to negligence and disregard of the construction safety rules, and consequently to the collapse of the concrete canopy on the people standing below.
Hrka said she was seeking accountability for the death of her son and the 15 other victims. She has also demanded that all detained protesters be released and that Vucic schedule an early parliamentary election as sought by the university students at the forefront of the demonstrations.
Vucic set up the loyalists' camp ahead of a major rally in Belgrade in March.
The enclosed zone colloquially known as "Caciland" apparently serves as a human shield for Vucic, filling a park and a street between his office and the parliament building.
Police have guarded the camp while the area has been off limits for the residents of Belgrade. A shooting incident there last month has triggered fears of violence.
Authorities have cracked down on the protesters in recent months, with hundreds detained and police breaking up protests.
Pro-government media and officials have branded protesting university students as "terrorists", accusing them of inciting violence.
