Greek Prime Minister Antonis Samaras was the first of the party leaders to vote in Sunday’s crucial election which is likely to see an anti-bailout party sweep to power.
Opinion polls put the left wing Syriza party in the lead with its plan to roll back austerity measures and demand part of the country’s huge debt be written off.
Samaras has warned that a win for Syriza could mean Greece would leave the euro and the country would miss out on the benefits of the EU’s huge quantitative easing programme.
The Greek economy last year emerged from recession for the first time in six years and unemployment has begun to drop slightly, but it may be years before the country recovers.
While Syriza is expected to form the biggest group in parliament, it is unclear whether it will be able to govern alone or have to form a coalition.
Polls opened at 7 a.m. (0500 GMT) and will close at 7 p.m. (1700 GMT). The first exit poll is expected immediately after voting ends.