Political parties supporting Greece's international bailout will begin forging a government on Monday after an election victory over radical leftists staved off the prospect of the debt-laden country leaving the euro and brought relief to global markets.

Conservative New Democracy leader Antonis Samaras called for broad support after winning Sunday's election over the radical SYRIZA party, which had threatened to cancel the aid deal in defiance of the country's lenders.

"There is no time to waste," Samaras told reporters in Athens as jubilant, chanting supporters waved blue party flags. "A national salvation government must bring economic growth and reassure Greeks the worst is over," he said.

With 99 percent of ballots counted, New Democracy had won 29.7 percent of the vote, ahead of SYRIZA on 27 percent. Samaras will need the support of the once-mighty PASOK Socialists, now humbled by angry Greeks, to form a government.

A 50-seat bonus given to the party which comes first would give New Democracy and PASOK 162 seats in the 300-seat parliament, in an alliance broadly committed to the 130 billion euros ($164 billion) bailout.

Relegated to third place in an earlier, inconclusive May 6 election, PASOK said it wanted a broad coalition that would include SYRIZA, but most important was to form a government and put an end to the political uncertainty battering Greece and world financial markets.

PASOK officials told Reuters that a party meeting on Monday would decide how the socialists would support Samaras - by participating fully in government, or by voting with the coalition in parliament.

The new government might get a helping hand from its euro zone peers with Germany's foreign minister suggesting Athens might get more time to implement the cuts demanded of it.

But most economists say even that would leave Greece, into a fifth year of deep recession, facing a program it cannot hope to deliver on.

The election result brought cheers and smiles at both the headquarters of New Democracy and SYRIZA. The leftists rode a huge wave of discontent over austerity and chronic corruption, viewing second place as a victory for a party that has long been on the fringes of Greek politics.

SYRIZA leader Alexis Tsipras, 37, made clear his was now the main opposition party, swearing to fight on against the bailout and take power sooner or later.

"Very soon, the Left will be in power," the former communist and student protest leader told elated supporters in central Athens after conceding defeat. "We begin the fight again tomorrow."