Serbs are voting in an election that is being seen as a test of the prime minister's proclaimed bid to lead the Balkan nation to the European Union.
The election comes amid an ultra-nationalist surge which favours close ties with Russia instead.
Prime minister Aleksandar Vucic called the election two years early, saying he needed a new mandate to press ahead with tough reforms demanded by the EU as the country faces deep economic and social problems.
But his opponents say he really wants to tighten his autocratic rule and win another four-year mandate while he is still popular.
The populist Serbian Progressive Party led by Mr Vucic, who has transformed from an extreme nationalist into a pro-EU reformer, is expected to win most of the 250 seats in parliament.
Whether Serbia remains firmly on the EU path, or sways away from it, will depend on whether the party gets enough votes to rule alone or if it has to form a coalition government with some anti-Western group.
“I am almost certain that we will carry on our European integration process and we will have to speed up the process of (EU) accession,” Mr Vucic said after voting on Sunday. “And of course, preserve our traditional ties with our friends (Russia) in the east.”
Mr Vucic added “that has to be one of the strategic, long-term decisions of the Serbian people and I’m not going to make any compromises with right-wing political parties”.
The right-wing revival has seen growing support for the Serbian Radical Party, headed by firebrand nationalist Vojislav Seselj, who is expected to return to parliament after being acquitted of war crimes by a UN tribunal.
Liberal, pro-Western opposition groups are fragmented and sidelined, struggling to reach the 5 per cent parliamentary threshold. They include a party led by former president Boris Tadic.
Mr Seselj has said the vote is a de-facto referendum on whether Serbia joins the “enemy” EU, or turns to some kind of a union with “our traditional ally Russia”.
“We can form a coalition only with the parties that will give up European Union (membership) and choose integration with Russia,” Mr Seselj said as he cast his ballot on Sunday. “These elections are very important for Serbia.”
While pro-Russian sentiments in Serbia are traditionally high because of close historic and cultural ties, many Serbs would also like to see their country reach the economic and democratic standards of the rich EU nations.
"Our membership in the European Union is something we have to fight for, because there is no other way for us," said Blazo Mitric, a Belgrade resident, as he cast his vote.
While no major surprises are expected, Sunday’s vote could tilt Serbia to the right.
Any rekindling of nationalism in the Balkans is considered more dangerous than in the rest of Eastern Europe because of the wars in the 1990s that claimed some 100,000 lives.
Western countries have sought to pacify Balkan nations by keeping them on track for EU membership. This could fail if Serbia gives up EU integration and turns to Russia instead, analysts say. There are 6.7 million voters in the election.
PA