Serbia's pro-European Prime Minister Aleksandar Vucic was set to win a landslide victory in Sunday's general election, according to initial projections.

Vucic's Serbian Progressive Party was on track to take 52.6 percent of votes, with the Socialists -- who have been in the ruling coalition since 2012 -- in second place with 12.9 percent, according to independent observing group CESID.

The far-right Radicals were also set to return to parliament after four years without seats, led by ultra-nationalist Vojislav Seselj who was recently acquitted of war crimes charges arising from the 1990s Balkan conflicts.

The Radicals were expected to win 7.4 percent, CESID said, clearing the five percent threshold and giving them a platform in parliament for their strongly anti-European and pro-Russian views.

Vucic, 46, had called the early election saying he needed a clear mandate to press ahead with the potentially unpopular reforms required to join the European Union.

But critics saw the vote as an attempt to consolidate power, expressing concerns about Vucic's authoritarian tendencies including curbs on media freedom.

A former Seselj ally turned pro-European centrist, Vucic said as he voted in Belgrade that he was "almost certain that we'll carry on our EU integration process," expressing hope that voters would choose a "European path".

He was due to speak to make a speech later on Sunday night.

Serbia, home to seven million people, opened the first stages in EU membership negotiations in December, although Brussels has said there will be no further enlargement of the bloc until 2020.

The election was Serbia's third in four years and enthusiasm appeared in short supply as voters queued at polling stations.

"We have elections too often," said retired Jelica Nikolic, 68, in Belgrade, saying she and her husband Radomir were voting more out of duty than conviction.

In the southwestern city of Novi Pazar, Edib Mahmutovic, 40, hoped the victors would "create new jobs that enable us to stay here and not have to look for a better life elsewhere in Europe".

- Reforms required -

It remained unclear how many other parties would enter parliament, with several of the fractured opposition groups hovering around the five percent parliamentary threshold in initial projections.

Powerful Vucic will now face the task of reforming inefficient state-run companies and the bloated public sector, measures required by the EU and as part of a loan agreement with the International Monetary Fund.

Serbia remains one of the poorest countries in Europe, with unemployment at about 20 percent and an average monthly wage of about 360 euros.

Hardliner Seselj -- who could now become the leading opposition figure in parliament -- ran a virulently anti-Western campaign, taking aim at Europe and also NATO for the 1999 bombing of Serbia during the Kosovo war.

At his last campaign rally, he said Serbia "will be safe only if it aligns with Moscow, which has always helped us and never bombed us".

Russia, a fellow Slavic and largely Orthodox Christian country, is seen as a supportive big brother figure by many Serbians -- especially for denying the sovereignty of Kosovo, which unilaterally declared independence from Serbia in 2008.

Although Vucic warned voters of the far-right threat, analysts say having hardliners in parliament could be a useful tool for the premier to present himself as a moderate leader.

"The Radicals' presence could be a good way for the Progressive Party to claim there is pluralism in Serbia," said Bojan Klacar at the Centre for Free Elections and Democracy.