Greeks are casting their ballots for a new parliament amid substantial voter activity, international media outlets report.

Unofficial exit poll results cited by various sources, including Novinite's Bulgarian-langauge website, suggest SYRIZA might already be having a clear lead on New Democracy, having garnered between 33.5 and 35.5 percent of the vote and New Democracy having 25.5-27.6 percent of the ballots so far cast in its favor.

Voting started at 07:00 EET (05:00 GMT) and ends at 21:00 EET. First official exit polls are expected shortly after polling stations close. There are 19 449 stations receiving voters on Sunday.

Early elections were triggered by three consecutive failures of lawmakers to elect a President in December. Greece's head of state, who has largely ceremonial functions, is elected by Parliament.

International attention is now nailed to Greece, with journalists from 45 countries having traveled to Athens for the election.

Most party leaders have already cast a ballot, with PM Antonis Samaras, the leader of New Democracy, having been the first of them to vote.

Sunday's election will "determine our future and our children's future," he told reporters. Samaras maintains that, under his government, Greece has been gradually pushing itself up after six years of recession.

PASOK Chairman Evangelos Venizelos, who is a junior coalition partner to Samaras, is quoted by Kathimerini as saying in Thessaloniki he hopes voters will "make choices that will lead to something better, not worse." The socialists who have lost their central role in Greece's politics after the debt crisis began are now hoping to jump over the three-percent threshold.

George Panandreou, ex-PM and leader of recently founded Movement of Democratic Socialists, voted before noon, repeating his stance that a referendum should be held on bailout reforms carried out in return of the EUR 240 B international loans.

At the same time Alexis Tsipras, whose leftist coalition SYRIZA is tipped to win the vote, surprised reporters with a comment in English after his statement in Greek, telling them that "Greece will return to democracy, social cohesion and dignity." In an EU elections debate in May, when he was among the contenders to head the EU Commission, he refused to speak in English and was the single participant to use an interpreter. 

The BBC quotes Tsipras as saying that "the vicious circle of austerity is over." Earlier he also declared that Europe's common future does not involve fastening belts. 

His plans to renegotiate the bailout terms under which Greece received its loans have fomented speculation that Athens might leave the Eurozone. In the past years SYRIZA's leader, however, has changed his stance with regard to the single currency, now insisting Greece should stick to the euro.