The head of radical leftist Syriza party Alexis Tsipras raises his fist to supporters after winning the elections in Athens January 25, 2015. [Photo/Agencies]

ATHENS - Greek leftist leader Alexis Tsipras promised on Sunday that five years of austerity, "humiliation and suffering" imposed by international creditors were over after his Syriza party swept to victory in a snap election on Sunday.

With about 92 percent of votes counted, Syriza was set to win 149 seats in the 300-seat parliament, taking 36.3 percent of the vote, 8.5 points ahead of the conservative New Democracy party of Prime Minister Antonis Samaras.

Samaras conceded victory but only the final result, expected in the early hours of Monday will show whether Syriza has won the 151 seats that would allow it to rule alone.

Nevertheless, the 40-year-old Tsipras is on course to become prime minister of the first euro zone government openly opposed to the kind of severe austerity policies which the European Union and International Monetary Fund imposed on Greece as a condition of its bailout.

"Greece leaves behinds catastrophic austerity, it leaves behind fear and authoritarianism, it leaves behind five years of humiliation and anguish," Tsipras told thousands of cheering supporters gathered in Athens.

Financial markets reacted nervously to the victory of Tspiras, who has promised to renegotiate Greece's debt agreements, fearing potential conflict with other euro zone governments that could put more strain on the currency bloc.

The euro slid to near an 11-year low and US stock futures fell as Asian markets opened on Monday.

Germany, Europe's biggest economy, has insisted Greece must respect the terms of its 240 billion euro bailout deal, which saved the country from bankruptcy but at the cost of bitter sacrifices by the Greek people.

As thousands of flag-waving supporters hit the streets of Athens, some shedding tears of joy, Germany's Bundesbank warned Greece it needed reform to tackle its economic problems.

Syriza's campaign slogan "Hope is coming!" resonated with voters worn down by huge budget cuts and heavy tax rises during six years of crisis that has sent unemployment over 25 percent and pushed millions into poverty.

"We hope our expectations will be fulfilled," said 47-year-old teacher Efi Avgoustakoushe. "On Monday in class, we're not allowed to comment and take sides but we will be smiling."