Opinion polls in Greece indicate millions of the country's voters were undecided before Sunday's polls.

The last voter surveys forecast victory for Tsipras' left-wing Syriza party over conservative New Democracy party chief Vangelis Meimarakis by margins ranging from 0.7 to 3 percentage points, the AFP news agency reported.

Both Tsipras and Meimarakis wrapped up campaigning on Saturday.

Tsipras resigned last month forcing early elections.

He won January's poll on an anti-austerity ticket, but had to accept economic reforms in exchange for a bailout from Greece's international creditors.

With nine parties hoping to enter parliament, whoever wins is unlikely to secure an outright majority and may need to form a coalition.

It has been a bruising year for Tsipras, who was elected on an anti-austerity platform in January but whose popularity plummeted after he agreed to a bailout deal worth up to $96 billion with Greece's eurozone creditors.

Tsipras agreed to the bailout after 61% of Greek voters in a July referendum overwhelmingly voted against an earlier offer that insisted on austerity measures.

The bailout Tsipras agreed to, which kept Greece in the eurozone, was widely seen as more severe than the original offer and included new taxes and spending cuts.

Tsipras resigned in August after the bailout split his ruling party, triggering Sunday's election.

While Tsipras' supporters say he went down fighting, Meimarakis has described his seven months in government as "an experiment that cost the country dearly".

In January Syriza won the general election with 36.34 percent of the vote, followed by the New Democracy bloc at 27.81 percent.

The ballot boxes for Greece's 10 million voters opened at 7am local time (4GMT).

Al Jazeera