ATHENS, Greece (AP) — Greeks were voting Sunday in a referendum on their nation's financial future, with opinion polls showing that residents were evenly split on whether to accept creditors' demands for more austerity in return for rescue loans or defiantly reject the deal.

Greek Prime Minister Alexis Tsipras was gambling the future of his 5-month-old left-wing government on the hastily called poll — insisting that a "no" vote would strengthen his hand to negotiate a better deal with creditors while a "yes" result would mean capitulating to their harsh demands.

The opposition accuses Tsipras of jeopardizing the country's membership in the 19-nation club that uses the euro and says a "yes" vote is about keeping the common currency.

While voters headed to polling stations, large lines once again formed at ATM machines. Worried Greeks were still withdrawing their daily limit of 60 euros ($67) — part of the banking restrictions imposed last Monday in an attempt to halt a bank run following Tsipras' call for a referendum.

"Today, democracy is defeating fear ... I am very optimistic," Tsipras said after voting in in central Athens, surrounded by dozens of journalists.

Tsipras' high-stakes standoff with lenders— the European Union and the International Monetary Fund — resulted in Greece defaulting on its debts this past week and shutting down its banks to avoid their collapse. The debt-wracked nation also lost access to billions of euros after an existing bailout deal expired.

The sense of urgency was palpable all week as Greeks struggled to decipher a convoluted referendum question while being bombarded with frenzied messages of possible impending doom.

Nikolaos Papadopoulos, a voter in Athens, said he cast a "yes" ballot.

"I believe in a democracy, in a united Europe, in a world with a good economy. And I want us all to work together to move forward and not to be retrogressive," he said.

But another Athens voter, Ioannis Nikolaou, disagreed.

"I voted for Tsipras and want to vote 'no' because I've lived in Europe and know what rights Europeans and Greeks have ... they don't have the same rights," he said.

Polls published Friday showed the two sides in a dead heat and that an overwhelming majority of people questioned — about 75 percent — wanted Greece to remain in the euro currency.

"Today, we Greeks decide on the fate of our country," conservative opposition leader Antonis Samaras said as he voted. "We vote 'yes' to Greece. We vote 'yes' to Europe."

Yale University political science professor Stathis Kalyvas said the Greek government will face daunting challenges no matter which way the vote goes.

If the "no" side wins, Kalyvas said other eurozone countries could refuse to negotiate a better deal for Greece because of their distrust of Tsipras.

A "yes" win won't mean a road to the negotiating table strewn with roses either, but would likely usher in a new government with a shot at negotiating an improved deal, Kalyvas said.

He said if the EU wants to keep Greece in the eurozone, it will have to come up with "a very generous plan" since the cost of the crisis has shot up to unanticipated levels.

German Finance Minister Wolfgang Schaeuble agreed, telling the daily Bild paper that future negotiations between Greece and its creditors will be "very difficult" because the country's economic situation has worsened dramatically in recent weeks.

Greek Finance Minister Yianis Varoufakis, meanwhile, launched a salvo at other euro nations. He accused them of holding out on a bailout deal to allow Greece's bank coffers to run dry so they could force Greece to accept what he called a humiliating deal.

Writing in the daily Kathimerini, Varoufakis said accepting creditors' terms would be a "permanent condemnation" while rejecting them would offer the "only prospect for recovery."

Varoufakis says banks will reopen Tuesday whatever the referendum's outcome. But that's unlikely to happen unless the European Central Bank agrees to increase credit to Greek banks.

Deputy Prime Minister Yiannis Dragasakis, meanwhile, denied media reports that he would be picked to lead a new "grand coalition" government after the vote.

"The country has a prime minister who will have an even stronger popular mandate and support. I will serve this mandate," he said.

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Online:

Official referendum website: http://www.referendum2015gov.gr/en/

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Associated Press writers Derek Gatopoulos, Iuliia Subbotovskaia and Eftehia Katsareas in Athens, Greece, contributed to this report.