Voting finished on Sunday in Greece's bailout referendum, with analysts suggesting voters had defied warnings from across Europe that rejection of the creditors' terms would set their country on a path out of the euro.

No exit polls were conducted, but three opinion polls by GPO, Metron Analysis and MRB all showed the 'No' camp' ahead by three points. A poll by Marc estimated 49.5 to 54.5 percent of Greeks voted "No" compared to 45.5 to 50.5 percent voting "Yes," based on surveys conducted through the week.

The polls were released after voting ended on Sunday because of a ban on the publication of polls on the day before a vote is held.

Nikos Filis, parliamentary spokesman for the ruling Syriza party said the result of the opinion polls would allow the government to move ahead quickly to reach a deal with creditors.

"I think this is guidance for the government," he said after the polls came out.

Athens' partners have warned over the past week that a "No" vote would mean cutting bridges with Europe and driving Greece's crippled financial system into outright bankruptcy, dramatically worsening the country's 5-year-long depression.

If confirmed, the result will also deliver a hammer blow to the European Union's grand single currency project. Intended to be permanent and unbreakable when it was created 15 years ago, the euro zone could now be on the point of losing its first member with the risk of further unravelling to come.

A "No" vote would leave Greece and the euro zone in uncharted waters. Unable to borrow money on capital markets, Greece has one of the world's highest levels of public debt. The International Monetary Fund warned last week that it would need massive debt relief and 50 billion euros in fresh funds.

Greece's leftwing government called the referendum only a week ago after it rejected the tough terms offered by international creditors as the price for releasing billions of euros in bailout funds.

Prime Minister Alexis Tsipras denounced the bailout terms as "blackmail" and declared that a "No" vote would strengthen the government's hand to get a better deal that would allow the banks to re-open this week.

French President Francois Hollande will meet German Chancellor Angela Merkel on Monday night in Paris to evaluate the consequences of the Greek referendum, according to a Sunday statement from the Elysee Palace.

"The meeting is part of the constant co-operation between France and Germany to find a durable solution in Greece," said the statement.

Greece will have to introduce another currency if it votes "No" in Sunday's referendum on its potential bailout terms, European Parliament president Martin Schulz said on German radio Deutschlandfunk.