Voting started Sunday in Serbian snap parliamentary elections with the country's course to European Union (EU) membership at stake.

The 6.75 million registered users are to choose from 22 tickets, but the crucial choice is between the ultra-nationalist Serbian Radical Party (SRS) and President Boris Tadic's pro-EU Democratic Party (DS), both tipped to win close to one-third of ballots cast.

Outgoing Prime Minister Vojislav Kostunica's Democratic Party of Serbia (DSS) is expected to remain in position of the kingmaker despite its dwindling popularity, with the late Slobodan Milosevic's Socialist Party of Serbia (SPS) in tow.

Local observers said a coalition of SRS with DSS and SPS was the most likely outcome. Kostunica and SRS leader Tomislav Nikolic have wowed to prevent Serbia's closer ties with EU in protest at Western support of Kosovo's secession from Serbia.

Another pro-European group, the Liberal-Democratic Party (LDP), has been tipped to be the fifth and final to clear the five percent hurdle of votes won to qualify for parliament, along with minority representatives.

The parliamentary poll, called three years early when Kostunica's and Tadic's alliance disintegrated in the tug of war over Serbia's course, is held together with the vote for municipal authorities.

The first estimates of the outcome are expected from agencies processing a sample of polling stations a few hours after the voting ends at 8 p.m. (1700 GMT).