The campaign was dominated by voter concerns over economic worries and immigration.
The FPO led opinion polls for months but its edge over the ruling Austrian People's Party (OVP) has shrunk to almost nothing as Chancellor Karl Nehammer casts himself as a statesman and depicts his rival, FPO leader Herbert Kickl, as a toxic menace.
Whoever wins will fall short of an absolute majority, polls show, but will claim the right to lead a coalition government.
The first polling stations opened on Sunday morning and projections are due minutes after polls close at 5pm, with results being finessed over the ensuing hours.
Chancellor Karl Nehammer says his party won't join a government with Herbert Kickl in it. (AP PHOTO)
"What's at stake is whether the FPO will appoint the chancellor or not," Kathrin Stainer-Haemmerle, political science professor at the Carinthia University of Applied Sciences.
"Should that happen, then I have to say the role of Austria in the European Union would be significantly different.
"Kickl has often said that (Hungarian Prime Minister) Viktor Orban is a role model for him and he will stand by him."
An FPO victory would make Austria the latest European Union country to register surging far-right support after gains in countries including the Netherlands, France and Germany.
The Eurosceptic, Russia-friendly FPO, which is critical of Islam and pledges tougher rules on asylum seekers, won a national vote for the first time in June when it beat the OVP by less than a percentage point in European elections.
The OVP, which like the FPO backs tougher immigration rules and tax cuts, is the only party open to forming a coalition with the far-right party.
However, Nehammer says his party will not join a government with Kickl in it.
President Alexander Van der Bellen, who oversees the formation of governments, has voiced reservations about the FPO because of its criticism of the EU and its failure to condemn Russia's invasion of Ukraine.
The party opposes EU sanctions on Moscow, citing Austria's neutrality.
He has hinted he might thwart Kickl, noting the constitution does not require him to ask the first-placed party to form a government, even though that has long been the convention.
The FPO wants to stop granting asylum altogether and build a "fortress Austria" preventing migrants from entering, even though that would be widely viewed as illegal or impractical.
Nehammer has depicted Kickl as a conspiracy theorist shouting from the sidelines while he runs Austria.
The 51-year-old Nehammer has since 2021 led a coalition with the left-wing Greens, but the alliance has proved fractious with the economy struggling and inflation worrying voters.
13°C