Greece's two main parties, which back tough austerity measures, have lost their parliamentary majority, throwing the country into political uncertainty.
Between them, Pasok and New Democracy attracted less than a third of the vote in elections on Sunday.
A radical left coalition (Syriza) came second after New Democracy, and a neo-Nazi party polled almost 7%.
Greece has secured two EU-IMF bailouts but the result is seen as a rejection of their stringent demands.
With about 99% of votes counted, centre-right New Democracy (ND) is leading with 18.9%, down from 33.5% in 2009.
ND and the socialist Pasok have between them run Greece since the 1970s. Since November, they have been in a coalition led by technocrat Prime Minister Lucas Papademos.
Pasok could only manage third place with 13.2%, down from 43.9% in the last elections and behind Syriza, which polled 1
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