ATHENS (AFP) - Polls opened nationwide in Greece's general election on Sunday, with the leftist Syriza party seeking to return to power in a neck-and-neck race against conservative New Democracy and a gauntlet of tough economic reforms looming.

Over 9.8 million Greeks were registered to vote in an election that will select a new government to implement a three-year bailout adopted by the country's Parliament last month. The divisive decision led to the toppling of the government of radical prime minister Alexis Tsipras.

Mr Tsipras was on Sunday fighting for a second chance to govern the struggling euro zone nation in the tense election that is proving too close to call.

The 41-year-old former premier headed into the contest with a slim lead in the polls over his 61-year-old conservative rival Vangelis Meimarakis, head of the New Democracy party.

But with around a tenth of the electorate estimated to be undecided, and the gap between the two parties under the 3 per cent margin of statistical error, pollsters say the race is too close to call.

The vote pits his radical left Syriza party against the conservative New Democracy bloc headed by tough-talking former lawyer and defence minister Vangelis Meimarakis, who has wiped out the gap between right and left during the election campaign.

Ballots close at 4pm GMT, at which point exit polls will be available.

The Interior Ministry is expected to make an announcement on the first official results after 6pm GMT.

The vote is the third this year for Greeks, who also cast ballots in an anti-austerity referendum in July, and the fifth in six years as Mr Tsipras seeks a fresh mandate to push through the tough reforms he agreed in July in return for a new 86 billion euro (S$136 billion) international rescue.

Many voters said they were casting their ballots with a heavy heart, knowing that whichever party wins, they will still be facing the tough reforms Mr Tsipras agreed in July in return for a new international rescue.

"I'm voting with great sadness," said Mr Nikos, a former engineer.

"My two children are unemployed and are living on my pension, which has been cut from 1,200 euros to 750 euros," he told Skai TV.

"I hope better days will come but I don't see it happening," he said.

"Whoever is elected the result will be the same," added Mr Yiannis, also a pensioner.

"Greece has been owing money for its entire existence, and as long as this happens it will suffer."

Mr Tsipras, a charismatic former student leader, was elected in January with 36.34 per cent of the vote, becoming Greece's youngest prime minister in 150 years and a beacon for anti-austerity campaigners across the European Union.

He took office as irate Greeks ran out of patience with the dire belt-tightening reforms imposed by the debt-hit country's international creditors. At the time New Democracy trailed well behind, winning 27.81 per cent of the vote.

But the latest figures now show Mr Tsipras leading Mr Meimarakis by a narrow margin, with polls putting the Syriza leader's advantage at between 0.7 per cent and 3.0 per cent.

It was his own cash-for-reforms deal with Greece's international lenders in July, signed days after Greeks overwhelmingly voted "No" to more austerity in a national referendum, that upset supporters.

A fifth of Syriza's MPs quit the party and set up a new one - Popular Unity - saying the deal to introduce more tax hikes and pension reforms in return for a massive international rescue was an unacceptable U-turn.

"He had no option, he did it because he had to, for the country," said retired former teacher Elias Pappas. "If we'd had to leave the euro zone instead, the consequences would've been far worse."

Helene, a waitress, added: "We need to give him a second chance. He's only had seven months in office."

Mr Tsipras was forced to call a new election to ensure a strong enough majority to implement the reforms. But in a slap in the face this week, his flamboyant former finance minister Yanis Varoufakis said he would vote for the breakaway hardliners rather than Tsipras.

As Mr Tsipras wound up his campaign on Friday, he said victory for Syriza would strike a blow for Europe's left.

"Do we want a Europe of austerity or one of solidarity and democracy?" the 41-year-old said. "The result will be a key message for Europe."

Dr Manolis Alexakis, a political sociologist at the University of Crete, says Greeks are weary after successive votes and never-ending austerity.

"People seem tired," he said. "The message is, please finish whatever should be done."

Even after Mr Tsipras' broken promises, many voters believe he has their interests at heart and represents a break with past leaders perceived as corrupt.

But Mr Meimarakis has cautioned voters against giving a second chance to a politician who publicly admitted he opposed the bailout he signed.

"Do you know of any other prime minister who brokered a deal, brought it to parliament, voted for it and signed it, whilst saying he does not believe in it?" Mr Meimarakis told the To Vima weekly.

"I fear that if Syriza is elected... the country will soon be led to elections again," said the bushy-eyebrowed 61-year-old who took the helm of New Democracy a couple of months ago.

But with nine parties hoping to enter parliament, no group is likely to secure an outright majority and Syriza could well need an ally from among those he despises.