Greeks have stunned the European Union by voting overwhelmingly to reject the austerity terms demanded by the country's international creditors.
With more than two thirds of the votes counted, finance minister Yanis Varoufakis said the Greek people had sent back the "ultimatum" from the eurozone and the International Monetary Fund (IMF).
The result - with more than 60% voting "no" - represents a sensational victory for the country's radical left prime minister Tsipras Alexis who had gambled all on the outcome of the referendum.
But it leaves the country facing an uncertain future – with opponents warning he needs a new bailout deal fast if he is to avoid a catastrophic financial crash that could send it spinning out of the single currency.
With Greek banks rapidly running out of cash, German Chancellor Angela Merkel and French President Francois Hollande – the leaders of the two biggest eurozone members – will meet tomorrow in Paris for crisis talks.
In London, David Cameron will meet with Chancellor George Osborne, Bank of England Governor Mark Carney and other senior officials to discuss the likely impact on the UK.
Although Britain is not part of the single currency bloc, Mr Osborne warned that it could not be insulated from any financial turmoil.
"Whatever Greece decides, Britain is prepared. We have the plans in place for whatever the outcome is," Mr Osborne told BBC1's The Andrew Marr Show.
"I don't think anyone should be in any doubt - the Greek situation has an impact on the European economy which has an impact on us. We cannot be immune from these developments."
In Athens, jubilant supporters of the Syriza government poured into Syntagma Square opposite the Greek parliament to celebrate what they regarded as a famous triumph and a decisive rejection of austerity.
Mr Varoufakis said the Greek government would now reach out to the institutions - the IMF, the European Commission, and the European Central Bank - to try to find an agreed way forward.
"With this 'no' we will try to co-operate with our partners and we will invite them one by one to see if we can find some common ground," he said.
However it was far from clear what appetite there would be among the creditors for fresh talks with trust on both sides apparently at rock bottom.