Greek voters on Sunday started casting ballots in a landmark referendum on terms of agreement with creditors on the next deal with the country's lenders.
The voting would determine whether Greece would avert a looming disorderly default or exit the Eurozone.
According to the Greek ministry of internal affairs and administrative reform, about 8.5 million people are eligible to vote in the referendum. It will be considered valid if at least 40 percent of registered voters participate in the vote, TASS news agency reported.
According to the International Monetary Fund (IMF), the Greek debt load is unsustainable and Greece needs a debt relief in exchange for reforms and a new 50-billion euro ($5.5 billion) financial package until 2018 to stay afloat.
Greek Finance Minister Yanis Varoufakis accused Athens' creditors of "terrorism" in an interview published on Saturday.
Greek Prime Minister Alexis Tsipras has urged citizens for a "No" vote, saying it would strengthen the government's hands in debt talks with creditors.
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"I call on you to say again a big and proud 'NO' to ultimatum," Tsipras said on Saturday during a rally staged in favour of the "No" vote.
On Thursday, the Leftist leader in an interview said he was confident that the reforms-for-cash debt deal Greece has been seeking for five months with creditors will be reached within 48 hours after Sunday's referendum regardless of the result.
However, European leaders say that such a result may well lead to Greece's exit from the Eurozone.