The Panhellenic Socialist Movement (PASOK) party, led by George Papandreou, was a close second in opinion polls published before a September 1 blackout.
Papandreou has attacked Karamanlis's New Democracy over its handling of the forest fires and claims it has widened the gap between the rich and poor, but it has still struggled to capitalise on the government's problems.
 
Forest fire victims

Barnaby Phillips, Al Jazeera's correspondent in Athens, reported that some people feel that the election should have been cancelled for the sake of the victim's families.
 
"Once they get elected, politicians don't care about the people, they only care about themselves"

Christina Bakou, undecided voter
"Many say the response to the fires was badly organised and slow and this is going to cost the government votes," he said.
 
"However, many blame the socialist opposition too, as it is argued that they failed to tackle corruption and inefficiency when they were in power."
 
The polls showed more than 10 per cent of Greek voters were undecided about which party they would back.
 
Many analysts say that these people, disillusioned by the two parties that have ruled Greece for more than 30 years, will probably decide the election.
 
Dimitris Sotiropoulos, a political analyst at the ELIAMEP foreign policy think tank, said: "Many are deciding in the last week, on the last day, in the last hour. This is a mass that will make a decision based on the economic benefits offered."
 
Christina Bakou, 41, an undecided voter in the central Greek town of Kirra, said: "Once they get elected, politicians don't care about the people, they only care about themselves."
 
Extensive reforms
 
Karamanlis has been praised by the European Union for cutting deficits and turning around Greece's economy, and he has vowed to push on with the reforms the country needs to catch up with its euro zone partners.
 
Greek per capita gross domestic product (GDP) is the lowest in the zone next to Portugal's and 20 per cent of the population live below the poverty line.
 
Meanwhile, unemployment, although down to 7.7 per cent in May, remains one of the region's highest, despite 4.4 per cent GDP growth in the first half of the year.
 
If it wins, PASOK is promising to promote a pro-business economic model coupled with strong social protection.
 
"We had such destruction as a result of the mistakes made by the government. Greek people have been affected, elections are close and we will win," Papandreou said.
 
Coalition slowdown
 
Meanwhile, Karamanlis, 51, has ruled out forming a coalition with the far-right Popular Orthodox Rally, which may enter parliament for the first time.
 
At least 65 people died in the fires that
swept across Greece last month [AFP]
"There is no chance of co-operation. The country will be led to new elections," he said. 
 
Whoever wins must urgently tackle a pension system that could collapse within 15 years.
 
Both parties have made pre-election pledges not to raise contributions or age limits, measures experts say are necessary.
 
Economic analysts say that Greece's EU commitments, such as balancing its budget by 2010, tie the election winner to maintaining existing economic policies.
 
"For the reforms it would be best if one party had a comfortable majority," Theodor Schoenebeck, an economist at Deutsche Bank, said.