Greek voters battered by years of crippling income and public-sector cuts punished the two mainstream parties on Sunday and gave no party enough votes to govern alone.
The abstention rate was close to a record-breaking 40 per cent. Voting is officially compulsory in Greece, although no sanctions are applied for not casting a ballot.
With more than 99 per cent of the vote counted the conservative New Democracy Party led with 18.9 per cent and 108 of parliament's 300 seats.
The Radical Left Coalition, or Syriza, knocked the centrist Panhellenic Socialist Movement (Pasok) into third place, winning 16.76 per cent and 52 seats.
Pasok saw its support slashed to 13.2 per cent, a historic low. It will have just 41 seats compared to 160 after the last election.
New Democracy party leader Antonis Samaras insisted that any coalition should renegotiate the terms of the country's loan deal with the "troika" -the International Monetary Fund, the European Central Bank and the European Commission.
"We are ready to take up the responsibility to form a new government to remain in the euro and to amend the terms of the loan agreements so that there is economic growth," he said.
Syriza leader Alexis Tsipras said that the troika deal should be overturned altogether.
"The people have rewarded a proposal made by us to form a government of the left that will cancel the loan agreements and overturn the course of our people toward misery," he said.
After receiving the mandate to start negotiations from Greek President Karolos Papoulias, Mr Samaras will have three days to strike a coalition deal.
But that could prove impossible because even with the support of Pasok New Democracy would fall two seats short of a governing majority.
If Mr Samaras fails to cobble together an administration, Greece faces new elections under a caretaker government in mid-June.
The right-wing anti-austerity Independent Greeks won 10 per cent and the Greek Communist Party 8 per cent.
The neonazi Golden Dawn, which has been involved in violent attacks on immigrants and ran on a chauvinist platform, got about 7 per cent of the vote - up from 0.29 per cent in 2009.
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