Greece's government on Sunday looked to have won a 'No' it had been seeking in a referendum on bailout terms, AFP reports.
An official tally of over half the ballots cast showed that a resounding 61 percent of Greek voters had backed the government's 'No' in the referendum.
Senior eurozone officials were to hold talks on Monday to discuss the result, a European source told AFP.
France's President Francois Hollande and German Chancellor Angela Merkel were to meet in Paris the same day to assess the result, the French presidency said. Hollande also spoke with Greek Prime Minister Alexis Tsipras by telephone late Sunday.
Merkel's deputy chancellor, German Economy Minister Sigmar Gabriel, said Greek Prime Minister Alexis Tsipras had "torn down bridges" between his country and Europe with the vote, according to the news agency.
New negotiations on a bailout were now "difficult to imagine," Gabriel was quoted as having told the Tagesspiegel newspaper.
Several EU leaders had said a 'No' vote could see an end to further bailout negotiations, forcing Greece to leave the 19-nation eurozone, and possibly even the European Union, in what has been termed a "Grexit".
Greece, however, insisted the result meant it was better placed now to demand its international creditors — the European Commission, European Central Bank (ECB) and the International Monetary Fund (IMF) — drop harsh austerity demands and accept a restructuring of its debt.
"With this result, the prime minister has a clear mandate from the Greek people," government spokesman Gabriel Sakellaridis said on television, according to AFP.
"Initiatives will intensify from this evening (Sunday) onward so that there can be a deal" on a new bailout, he said.
Defense Minister Panos Kammenos, who also leads the junior coalition party in Prime Minister Alexis Tsipras's leftwing government, said in a tweet that the Greeks "proved they don't bow to blackmail, to threats".
Tsipras said as he cast his own ballot in Athens that "no one can ignore the will of the people to live, to live with determination, to take its destiny into its own hands", according to AFP.
Greece was officially declared in default on Friday by the European Financial Stability Facility, which holds 144.6 billion euros ($160 billion) of Greek loans, after Athens missed an International Monetary Fund (IMF) repayment.
Tsipras has called for the ECB, IMF and European Commission to forgive 30 percent of the 240 billion euros ($267 billion) they have loaned Greece over the past five years, and allow it a 20-year grace period before it starts repaying the rest.