A radical left-wing party vowing to end Greece's painful austerity program won a historic victory in Sunday's parliamentary elections, setting up a showdown with the country's international creditors that could shake the eurozone.

Greek Prime Minister Antonis Samaras conceded defeat to the anti-austerity party Syriza in general elections, and said he hoped the new government would not endanger the country's membership in the European Union and eurozone.

"I hand over a country that is part of the EU and the euro. For the good of this country, I hope the next government will maintain what has been achieved," Samaras said in a brief address to reporters after exit polls pointed to a victory for the radical left-wing Syriza party.

Alexis Tsipras, leader of the communist-rooted Syriza party, immediately promised to end the "five years of humiliation and pain" that Greece has endured since an international bailout saved it from bankruptcy in 2010.

"The verdict of the Greek people ends, beyond any doubt, the vicious circle of austerity in our country," Tsipras told a crowd of rapturous flag-waving supporters.

Syriza appeared just shy of the majority that would allow it to govern alone. With 97.6 percent of polling stations counted, Syriza had 36.4 percent — and 149 of parliament's 300 seats — versus 27.8 percent for Prime Minister Antonis Samaras' conservatives.

The far-right Golden Dawn and pro-European To Potami parties are in a neck-and-neck race for third place with percentages between 6.4 and eight percent respectively, according to polls.

The Interior Ministry said that its projections, based on early returns, show Syriza gaining 150 of parliament’s 300 seats. But it added that the margin of error meant that the final number could be 149 to 151. A final tally will not be announced until early Monday.

If Tsipras, 40, can put together a government, he will be Greece's youngest prime minister in 150 years, while Syriza would be the first radical left party to ever govern the country.

The prospect of an anti-bailout government coming to power in Greece has revived fears of a bankruptcy that could reverberate across the eurozone, send shockwaves through global markets and undermine the euro, the currency shared by 19 European countries.

The already battered euro was down 0.3 percent Monday, at $1.117, on the news of Syriza's victory. That was its lowest since April 2003.A radical left-wing party vowing to end Greece's painful austerity program won a historic victory in Sunday's parliamentary elections, setting up a showdown with the country's international creditors that could shake the eurozone.

Financial markets have been worried that a Syriza victory could trigger a new financial crisis in Greece, but the repercussions for the eurozone are expected to be far smaller than feared the last time Greeks went to the polls in 2012.

Tsipras has promised to renegotiate the country's $270 billion international bailout deal. He has pledged to reverse many of the reforms that creditors demanded in exchange for keeping Greece financially afloat since 2010.

The anti-bailout rhetoric has renewed doubts over Greece's ability to emerge from its financial crisis that has seen a quarter of its economy wiped out, sent unemployment soaring and undermined the euro, the currency shared by 19 European countries.

Greece's creditors insist the country must abide by previous commitments to continue receiving support. Greece could face bankruptcy if a solution is not found, although speculation of a "Grexit" – Greece leaving the euro – and a potential collapse of the currency has been far less fraught than during the last election.