Greeks vote in parliamentary elections. Reuters

Governing parties backing EU-mandated austerity in Greece are on course for a major drubbing as hard-hit voters, venting their fury in elections, defected in droves, according to exit polls.

In a major upset that will not be welcomed by the crisis-plagued country's eurozone partners, the two forces that had agreed to enact unpopular belt-tightening in return for rescue funds appeared headed for a beating, with none being able to form a government.

After nearly 40 years of dominating the Greek political scene, the centre-right New Democracy and socialist Pasok saw support drop dramatically in favour of parties that had virulently opposed the tough austerity dictated by international creditors.

The latest figures showed New Democracy leading with between 19 – 20.5% of the vote, followed by the radical leftist party, Syriza, with as much as 17% and socialist party Pasok with between 13 – 14 %. And for the first time since the collapse of military rule, ultra-nationalists were also set to enter parliament with polls showing the neo-Nazi Chrysi Avgi (Golden Dawn) capturing as much as 8%.

With the nation wrestling its worst crisis in modern times, the big winner appeared to be Syriza, which had campaigned ardently against austerity and was poised to become the second biggest party in Athens's 300-seat House.

A Metron analysis poll showed the leftists gaining as much as 18.5%, more than the mainstream Pasok lead by former finance minister Evangelos Venizelos, who negotiated the latest €130bn (£105bn) loan agreement reached between Athens and the EU and IMF.

"That agreement now belongs to the past. It has been delegitimised," said Panaghiotis Lafazanis, a prominent Syriza MP. "Our strong showing sends a message especially to Europe that Greeks have rejected austerity."

Lafazanis said Syriza would keep to its pre-election pledge to form a government of "the united left" that would work to stop the fiscal remedies meted out to Athens by its EU partners.

The election, called by Lucas Papademos, the technocrat prime minister overseeing an emergency coalition for the past six months, is the most critical in decades. Not since the restoration of democracy in 1974 has so much been at stake, with politicians and analysts alike saying Greece's political stability and future in the eurozone would rest on the result.

The significance of the moment did not appear to be lost on Greeks. From early in the morning voters, many dressed in Sunday best, filed into the thousands of public schools serving as polling stations.

"I hope my vote will be for the good of my country," said Georgios Kladis, holding his grandson's hand. "Greece has to be governed. I hope that will be possible tomorrow."

Although elections are traditionally seen as a joyous affair, the pinnacle of democracy for a deeply politicised nation, volunteer lawyers working as election monitors in Athens reported voters as being in sombre mood. Many were said to have spent an "inordinately long time" in curtained-off booths before deciding which candidate to back.

Visibly moved, Fotis Kouvelis, who heads the small Democratic Left party, said: "We are voting to keep Greece alive and society intact."

"People are clearly troubled," observed Dimitris Anastasopoulos, a monitor at a polling station in one of the capital's leafy northern suburbs. "We've had some in booths for 10 minutes. It's got to the point where we've had to remind them there is a queue outside."

Pulling up at another polling station on his bicycle in shorts and sandals, Orestis Papadopoulos said he was excited to be among the 110,000 Greeks voting for the first time. "If you asked me whether I'd vote even a few months back I would have said 'bah, no way,'" he said. "But this is critical. First they put a pistol to our heads, now they're shoving it down our throats. All this austerity has been for nothing. It doesn't work. And I want to add my voice to those people saying 'no'."

Maria Stasini, 43, emerging from a polling station in central Athens, was also voting against the austerity measures. "It was a purely anti-austerity vote because all these measures have killed us," she said.

"My son has been unemployed for the past two years. He has sent out 400 emails and hasn't got even one reply.

"My husband is a plasterer and work for him has dropped by 80%. On top of everything, they pummel us with taxes," she said, adding she had been forced to close her restaurant last year.

"We were all New Democracy voters but how can we vote for them now when they, too, back such measures?"