With more than three-quarters of votes counted, results show Greeks have rejected the terms of international bailout by 61 percent to 38 percent.
Voters had been asked on Sunday whether to accept or reject the country's multi-billion euro bailout deal with the European Union.

Polling booths closed at 16:00 GMT on Sunday, with ten million Greeks eligible to vote.
With 97 percent of the total votes counted, the "No" vote was leading with 61.4 percent, against 38.7 percent for the "Yes" vote.
Greece's Prime Minister Alexis Tsipras said the rejection of the bailout deal meant creditors would be forced to address the question of easing the country's massive debt.
"This time, the debt will be on the negotiating table," he said in a televised address, insisting that an International Monetary Fund report seen this week "confirms Greek views that restructuring the debt is necessary".
Tsipras said that the referendum results did not mean Athens was headed for a so-called Grexit.
"This is not a mandate of rupture with Europe, but a mandate that bolsters our negotiating strength to achieve a viable deal," AFP news agency quoted him as saying.
Country's Finance Minister Yanis Varoufakis said the 'No' vote was a resounding "yes to a democratic Europe" adding that the government would call on partners to find common ground with Greece.
Meanwhile, Varoufakis is conferring with the country's bankers over what to demand next from the European Central Bank, a ministry spokesman confirmed to the AP news agency.
Greece's ruling Syriza government had closed the country's banks and imposed capital controls until July 6 to stem the flood of withdrawals after the bailout deal failed.
The cash-strapped nation eventually defaulted on an IMF payment of $1.8bn on June 30.
Soon after the results came out, Greece's conservative opposition leader, Antonis Samaras, who had campaigned for a 'YES' vote, resigned.
Al Jazeera's Barnaby Phillips, reporting from Athens, said the result shows a "much better" outcome for Tsipras and could embolden the prime minister to go back to Europe and demand a better deal for Greece.




Eurozone nations will hold a summit on Tuesday to discuss the referendum result, EU President Donald Tusk said, after the German and French leaders called for a meeting.
"I have called a EuroSummit Tuesday evening at 18h (1600 GMT) to discuss situation after referendum in Greece," Tusk said on Twitter after the referendum.
The AFP news agency reported that French President Francois Hollande will meet German Chancellor Angela Merkel in Paris on Monday.
The European Commission in a short statement said it "respects" the result of the Greece bailout referendum.
Commission president Jean-Claude Juncker will hold a teleconference on Monday morning with European Central Bank chief Mario Draghi and Jeroen Dijsselbloem, the head of the Eurogroup of eurozone finance ministers, the statement added.


Juncker will also be "consulting tonight and tomorrow with the democratically elected leaders of the other 18 eurozone members as well as with the heads of the EU institutions," it added.
Dijsselbloem on his part said it was up to Greek authorities to come forward with new plans after voters rejected bailout terms in the referendum result he called "very regrettable" for the future of Greece.
"For recovery of the Greek economy, difficult measures and reforms are inevitable. We will now wait for the initiatives of the Greek authorities.
Earlier, senior German conservative leader Michael Fuchs told the Reuters news agency that the Greek prime minister had caused a "disaster".