At stake is the pace of economic and social reforms needed for Greece to catch up with its euro zone partners.

Elections were due by March 2008 but Karamanlis had come under pressure from ministers to go to the polls early as the ruling party's popularity fell over a series of scandals and destructive forest fires.

The ruling New Democracy party, which swept to power in 2004, ending 11 years of socialist rule, has been praised by the European Union for turning the economy around, cutting deficits and pushing with reforms and privatisations.

But it has faced increasing protests at home over unpopular economic belt-tightening measures, slow social reforms and a series of political and economic scandals.