Greeks on Sunday will elect a "fighting government" and usher in a "new era" of reform, leftwing former premier Alexis Tsipras said as voting opened in the country's fifth general election in six years.

"The Greek people... will take their future into their own hands... and seal the transition to a new era," Tsipras said after casting his ballot in the working class Athens district of Kypseli.

The 41-year-old Syriza party leader said Greeks would elect "a fighting government" ready for the "confrontations necessary to move forward with reforms" and make the country a "powerful and equal partner in Europe."

Polls opened at 0400 GMT in the cliffhanger vote pitting Tsipras's radical left Syriza party against the conservative New Democracy bloc headed by tough-talking ex-lawyer and defence minister Vangelis Meimarakis, who has narrowed the gap between right and left during the election campaign.

Over 9.8 million Greeks were registered to vote in an election that will select a new government to implement more tough reforms demanded by EU leaders. Divisions over the three-year bailout adopted by the country's parliament last month led to the toppling of Tsipras's government.