Greece's charismatic leftwing leader Alexis Tsipras romped to victory in Greece's general election Sunday, winning his second mandate as premier this year despite a controversial austerity deal struck with European leaders.

With over 70 percent of the votes counted, Tsipras' Syriza party won 35.46 percent of the vote compared to 28.27 percent for conservative New Democracy and -- in a sense of deja vu -- will again form a coalition government with the small nationalist Independent Greeks (ANEL) party.

As results showed the radical 41-year-old pulling ahead after a tight race shadowed by painful tax rises and pension reforms that lie around the corner, New Democracy leader Vangelis Meimarakis admitted defeat.

"It appears that Mr Tsipras' Syriza is first, I congratulate him," said the 61-year-old lawyer and former defence minister, whose defeat signals the end of a decades-long era in which the conservatives and socialists alternated in power.

Turnout stood at 56 percent, slightly less than in January when six out of 10 voters cast their ballots, the interior ministry said.

In a victory speech to hundreds of cheering flag-waving supporters who turned out in evening heat on a central Athens' square, Tsipras said the victory would "turn the wheel" and "change the balance" in Europe.

When elected in January he became Greece's youngest prime minister in 150 years on taking office and a beacon for anti-austerity campaigners across the European Union.

"Europe will not be the same after our people's victory (on Sunday)," he said before supporters broke into Italy's revolutionary anthem, Bandiera Rossa, Italian for "Red Flag".

But Tsipras also admitted that the country's pledge to go forward with four years of painful reforms set out by Europe's leaders would not be easy.

"We have difficulties ahead," he told supporters. "Recovery cannot come through magic but through lots of work, stubbornness and struggle."

France's President Francois Hollande and European Parliament president Martin Schulz, both leftwingers too, congratulated the premier-elect on his win.

"Greece will have a period of stability with a solid majority," Hollande told.

But the new coalition is likely to have a slightly narrower majority of 155 seats in the 300-seat parliament, compared to 162 seats over the period from January to August, initial results showed.

Hands-down winner of a January general election, then with 36.34 percent of the vote, Tsipras resigned in August and called snap elections, gambling crisis-weary Greeks would give him a new mandate despite his contentious bailout deal with European leaders.

After winning office on an anti-austerity ticket, he agreed in July to more punishing austerity for the nation in exchange for its third financial rescue in five years.

He later argued he had effectively saved Greece from a chaotic exit from the eurozone.

But the move alienated many Syriza supporters and split the party, with a fifth of its anti-euro hardline MPs walking out, forcing Tsipras to call Greece's fifth general election in six years.

He went to the polls facing a strong challenge from conservative leader Meimarakis, who had slammed the former premier's U-turn with the country's creditors and his chaotic months in power.

Over 9.8 million Greeks were registered to vote for a new government which will face the tough task in the next weeks of pushing through the belt-tightening reforms agreed under the three-year bailout accord adopted by parliament last month.

The reforms come in return for a new 86-billion-euro ($97-billion) international rescue.

Signed days after Greeks overwhelmingly voted "No" to more austerity in a national referendum, the cash-for-reforms deal proved controversial, and Sunday many voters went to the polls with a heavy heart.

"Greeks wanted to try out Syriza but saw the results, they're a bunch of liars," 58-year-old conservative voter Marika Geraki told AFP.

But despite the broken promises, many voters believed Tsipras had their interests at heart and represented a break with past leaders perceived as corrupt.

"We want to be done with thieves, first the Germans and then the conservatives and socialists," 63-year-old Efthymia Xanthou told AFP.

Economic analysts responded positively to Tspiras' win. "Greek voters now seem to have given him the chance to do better," said Berenberg's Holger Schmieding.

"After years of almost unprecedented crisis, the vast majority of Greeks are endorsing parties that are promising to keep the country in the euro even if that implies thorough and painful reforms," he said.

Of the nine parties hoping to enter parliament, eight seem headed to win seats in the next parliament.

Partial official results showed neo-Nazi party Golden Dawn again in third place with 7.01 percent of the vote, followed by the Pasok socialists who garnered 6.37 percent.

Centrist To Potami party is likely to finish with a mere 3.65 percent, while the small anti-corruption Centrist Union party will exceed 3.0 percent and enter parliament for the first time.

Nearly 45 percent of Greeks sat out the election -- the third vote for Greeks this year including a referendum on austerity -- a significant rise in the previous abstention rate of 36 percent in January.