ATHENS - Greece's government claimed Sunday "a clear mandate" for less stringent bailout conditions as voters looked set to overwhelmingly back its rejection of further austerity in a key referendum.

It remained to be seen, however, how European leaders and institutions would view the likely result -- and whether it would trigger "Grexit", or Greece's exit from the eurozone, as some had warned.

Senior eurozone officials were to hold talks on Monday, a European source told AFP, without elaborating.

France's President Francois Hollande and German Chancellor Angela Merkel were also to meet in Paris the same day to discuss the result of the referendum, the French presidency said.

Early official figures, based on nearly 50 percent of ballots counted, showed 60 percent of votes in favour of a government's 'No' to tough austerity conditions that had been attached to a bailout deal that expired last Tuesday. Forty 40 percent had voted for 'Yes'.

The interior ministry said turnout was over 50 percent.

"With this result, the prime minister has a clear mandate from the Greek people," government spokesman Gabriel Sakellaridis said on television.

"Initiatives will intensify from this evening (Sunday) onward so that there can be a deal" on a new bailout, he said.

He added that the Bank of Greece was immediately asking the European Central Bank to inject emergency euro cash for Greece's depleted banks, which have been shuttered all week because of capital controls.

Defence 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".

However, in the street, some voters who had voted 'No' against further grinding austerity said they had been confronted with an impossible choice.

One of them, Nika Spenzes, 33 and unemployed, said: "I'm not happy - we cannot be happy as a nation with this unemployment and poverty. And a 'No' victory doesn't mean there's any more hope for Greece than before."

Even the 'Yes' voters were ambivalent about their camp's apparent defeat.

Paris, a 41-year-old dentist who had voted 'Yes', said that "I respect the Nos... they represent the suffering Greek people". She added: "I cannot honestly say I'm sad if the Nos have won because there's no real hope either way."

Costa, a 58-year-old architect who had voted the same way, said: "I'm not pleased but I'm pleased nearly half of Greeks voted for 'Yes'."

He added that he was "amazed by the huge amount of goodwill expressed to us in Europe despite the behaviour of our government, and I really hope it continues despite the referendum result. I think this government's days are numbered."

A pro-government crowd buoyed by the result began gathering in central Athens late Sunday to celebrate the likely 'No' result.

Tsipras, who had staked his political career on the outcome, had 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".

His most pressing problem, though, was to ease capital controls his government ordered to stem a bank run that had been rapidly draining bank deposits.

The measure, implemented after his announcement a week ago that he had suspended bailout talks to hold the referendum, has limited ATM card holders to daily withdrawals of just 60 euros ($67) a day.

Panic at that step, and at fears of Grexit, also prompted citizens to stock up on non-perishable food, medicine and imported goods, clearing out supermarket shelves.

The Greek banks' liquidity was expected to dry up entirely within a day or two unless the ECB -- a major creditor -- injected funds quickly through the Emergency Liquidity Assistance (ELA) mechanism.

The Euro Working Group, which comprises top treasury officials who prepare meetings for the Eurogroup of finance ministers from the 19-country currency union, will hold a meeting Monday to discuss the referendum.

Martin Schulz, the head of the European Parliament, though scathing of Tsipras's actions, told Germany's Welt am Sonntag newspaper that Europe could give short-term emergency loans to Greece "so that public service can be maintained and needy people get the money they need to survive".

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 IMF repayment.

Tsipras has called for much more than that, demanding the ECB, IMF and European Commission 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.