The far-right Freedom Party (FPÖ) and Social Democrats are competing for second place, opinion polls suggest.
The Social Democrats led the outgoing coalition with the ÖVP.
Immigration has been a dominant issue in the campaign and the FPÖ is thought to have its best chance in years of returning to government.
The party narrowly missed out on the presidency in December when Norbert Hofer was defeated by Alexander Van der Bellen, head of the Greens, who won with about 53% of the votes.
The election comes amid anxiety in Europe over the huge influx of undocumented migrants and refugees in 2015, which fuelled an electoral breakthrough by the far right in neighbouring Germany last month.
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