Greek voters have dealt a blow to eurozone hopes that Athens will stick to its austerity commitments as parties opposing more cuts, including neo-Nazis, won almost 60 per cent support at the polls.
According to updated exit polls, the two main parties suffered heavy losses on Sunday, with the conservative New Democracy and the left-wing Pasok getting just 32 to 34.5 per cent between them, down from 77.4 per cent at the last polls in 2009.
New Democracy, led by Antonis Samaras, remained the largest party but it fell short of an absolute majority in parliament.
It would therefore be tough for Samaras, once he is officially tasked to do so by the president, to form a government able to keep its austerity promises and implement more cuts demanded by the country's creditors.
Athens has already committed to finding next month another 11.5 billion euros ($A14.8 billion) in savings through 2014.
New Democracy obtained about a fifth of support this time, short of the 37 per cent needed for an absolute majority in parliament and down from 33.5 per cent three years ago.
The other main player Pasok saw its score slump to 13-14 per cent from 43.9 per cent. The party even looked set to be relegated to third place by the leftist Syriza, which scored 15.5-17.0 per cent, more than triple the 4.6 per cent of 2009.
"The ruling parties have been struck by an earthquake. It has crushed Pasok and sent a strong tremor through New Democracy," shadow foreign minister Panos Panagiotopoulos said on television channel Mega.
Panayotis Petrakis, economics professor at Athens University, expressed hope, however, that new French president-elect Francois Hollande "would prevent Europe treating us too harshly. There is still a little room for manoeuvre."
Petrakis told AFP the most likely outcome was another "government of technocrats" headed again by outgoing premier Lucas Papademos, or fresh elections.
Evangelos Venizelos, Pasok leader and the finance minister who negotiated the second bailout, called for a "national unity government" among pro-European parties but admitted this might be "clearly difficult."
Neo-Nazi party Golden Dawn was also set to enter parliament for the first time since the end of the military junta in 1974, with 6.5-7.5 per cent, making it the sixth-biggest party in the 300-seat chamber with some 20 lawmakers.
Leader Nikos Michaloliakos said his party would fight against "world usurers" and the "slavery" of an EU-IMF loan agreement he likened to a "dictatorship".
"The time for fear has come," he said.
The fourth-biggest party was set to be Independent Greeks with 10-11 per cent, a new right-wing party set up by New Democracy dissident Panos Kammenos, followed by the communist KKE on 8.0-9.5 per cent.
The Democratic Left, a Europhile new leftist party, notched up 5.5-6.5 per cent. In total seven parties were set to enter parliament compared with just five after the last election.
Both Pasok and ND have said they want the "troika" of the European Union, International Monetary Fund and European Central Bank to cut Greece more slack in their two bailout deals worth worth 240 billion euros ($314.0 billion).
But with voters angry at the austerity cuts demanded in response, many of the smaller parties, including possible kingmaker Syriza, want to tear up the agreements.
In ominous comments widely quoted by Greek newspapers on Saturday, German Finance Minister Wolfgang Schaeuble said that if Greece's new government deviated from its commitments, the country would "bear the consequences."
"Membership of the European Union is voluntary," he said in Cologne.
As a result, it is Greece's vote rather than France's presidential election, won by Hollande on Sunday, which "weighs heavier" on investors' minds, Valerie Plagnol, Credit Suisse director of research, said last week.