Greece was in a "critical" situation on Monday after an anti-austerity vote and a government had to be formed swiftly, the speaker of parliament said as he delivered the ballot's official results.

"These are critical times that require critical decisions," parliament chief Philippos Petsalnikos told reporters after briefing the head of state, President Carolos Papoulias.

"The country must remain standing within the EU, within the eurozone, the country must be governed," he said.

The conservative New Democracy party will be invited by Papoulias to form a government later Monday after topping the lists with an anaemic 18.85 percent of the vote, a result that gives it 108 deputies in the 300-seat parliament.

Party leader Antonis Samaras will then have three days to find allies before the mandate passes to the second party, leftist Syriza.

"I wish party leaders will rise to the level of the requirements and the responsibilities that we all have toward the country and citizens," Petsalnikos said.

Syriza wants to reject Greece's loan agreement with the European Union and the International Monetary Fund which has brought two years of salary and pension cuts and soaring unemployment.

The leftists garnered 16.78 percent of the vote and will have 52 deputies, Petsalnikos said.

The once-mighty Pasok socialist party fell to third place with 13.18 percent and 41 deputies, followed by the nationalist Independent Greeks party which tallied 10.6 percent, the equivalent of 33 lawmakers.

The Communist party won 8.48 percent of the vote and 26 seats, and the neo-Nazi Golden Dawn party grabbed 6.97 percent, enough for a presence in parliament with 21 deputies for the first time in Greece's political history.

A Europhile leftist party that also opposes the EU-IMF bailout, Democratic Left, rounds off the list with 6.1 percent of the vote and 19 seats.