Greece has started voting in an early general election that threatens to turn its decades-old political system on its head and bring the eurozone crisis back with a vengeance.

After two years of austerity cuts, polls indicate that voters are set to punish Greece's two main parties for having accepted yet more belt-tightening in return for two bailouts worth 240 billion euros ($308 billion).

That prospect worries international lenders, including the European Union and the International Monetary Fund, who fear that the resulting political instability could plunge the eurozone back into the mire.

Both the Pasok socialist party and the New Democracy conservatives, the dominant political forces for the past four decades, look likely to lose votes to around 30 smaller parties, some fiercely hostile to further cuts.

"We need to break from this corrupt political system of lackeys of foreign imperialism," Petros Alachmar, 31, an activist from the far-left Syriza party, said.

"We have had enough of austerity measures."

But with Athens already committed to finding in June another 11.5 billion euros in savings through 2014, any ambition to renegotiate terms "suggests a degree of liberty they do not have", Swiss bank UBS said in a research note.

Instability to continue

Greece has already written off a third of its debts and is in its fifth year running of recession.

One in five workers is unemployed, its banks are in a precarious position and pensions and salaries have been slashed by up to 40 per cent.

Voters are also fed up with decades of corruption and cronyism.

And immigration has become an issue, raising the prospect that the neo-Nazi Golden Dawn, with a swastika-like emblem and an admiration for Hitler, may enter parliament.

Pasok and New Democracy want the "troika" of the European Union, International Monetary Fund and European Central Bank to cut Greece more slack in their bailout deals.

But for many smaller parties this does not go far enough.

New Democracy is expected to win the most votes, but not enough for leader Antonis Samaras to govern without partners. One might be Pasok, its current partner in a stop-gap coalition. Another possibility might be fresh elections.

But for the markets and international lenders, the main fear is the implications for the battered eurozone.

Holger Schmieding, economist at Germany's Berenberg Bank, said there was a 40 per cent risk of Greece leaving the eurozone this year, with a "high" chance that no stable government willing to implement more reforms could be formed.

AFP