The protestors chanted “Vucic thief” as they marched peacefully through the city centre in the fourth such protest in as many weeks, according to Reuters.
The opposition movement - Protest Against Dictatorship - are calling for electoral reform and freedom in the media and against what they see as an increasingly autocratic rule by the sitting president.
“I support these people, my people, my country, against the dictatorship and the violence conducted by the government,” says protestor Dalibor Kocic.
“Everything is wrong,” added another protestor Natasha Vranic. “We don’t have freedom in the media. We don’t have freedom for journalists.”
Backers of the Alliance for Serbia, an opposition grouping of 30 parties and organisations, say Vucic is an autocrat and his party is corrupt, something its leaders vehemently deny.
Protesters leading the march carried a banner reading "#1OF5MILLION" in reference to an earlier statement by Vucic that he would not bow to demands even if five million protesters took to the streets.
The protests were ignited when a leader of the opposition Serbian Left party, Borko Stefanovic, was assaulted at an opposition meeting in the city of Krusevac in late November.
It then developed into a broader call for an end to political violence and for free and fair elections.
A week ago, there were an estimated 35,000-40,000 people on the streets – this time the number has risen to 50,000 according to local media.
President Vucic has denied all accusations of involvement in the attack on the politician that started the protest.
Vucic has also said he is ready to go to the polls and call another vote. He added that even if five million people protest, he would still not meet the demands of the protest movement and the opposition.
Serbia has a population of seven million.
According to a poll by the Belgrade-based CESID election watchdog in October, Vucic’s party holds 53.3% of the electorate while other parties are trailing far behind.
The SNS-led ruling coalition has a comfortable majority of 160 deputies in the 250-seat parliament. The next national election is scheduled for 2020.
For nearly a month, thousands of people have taken to the streets in weekly protests. This has raised the question of if the opposition movement can keep the momentum going and more importantly if the sitting government - and President Vucic - will listen and react to the call for change.
Following the breakup of Yugoslavia in 1992, Vucic joined the far-right Serbian Radical Party (SRS), whose core ideology is based on Serbian nationalism.
As president of Serbia, Vucic has adopted pro-European values and set Serbia’s membership in the European Union as the country’s strategic goal. Vucic also maintains close ties to Russia and China.