A tsunami of capital flight from Greece threatens to overwhelm the authorities, forcing the country out of the euro before fresh elections in June.

Economists warned that the Greek financial system could crumble within weeks or days unless the European Central Bank steps up support.

President Karolos Papoulias told party leaders that banks had lost €700m in withdrawals on Monday alone as citizens rush to pre-empt capital controls and a much-feared return to the Drachma.

He cited central bank warnings that "great fear" might soon escalate to panic. The leaked details lend credence to claims that capital flight by both savers and firms have reached €4bn a week since the triumph of anti-bailout parties on May 6.

Steen Jakobsen from Danske Bank said outflows are becoming unstoppable, not helped by open talk in EU circles of `technical’ plans for Greek withdrawal.

"This has a self-fulfilling prophecy built into it and I don’t think we can get to June. The fuse is burning and the only two options now are a controlled explosion where Germany steps in to ensure an orderly exit, or an uncontrolled explosion," he said.

The damage to the rest of Europe from Greece leaving the euro would be "somewhere between catastrophic and Armageddon", the chief negotiator for the body representing private sector holders of Greek bonds said on Wednesday.

Charles Dallara, who as head of the International Institute of Finance (IIF) spent months in Athens negotiating the largest ever sovereign debt restructuring, also said he had seen evidence that more people were moving their cash out of Greece.

"There has been a pick up of deposit flight from Greece," Mr Dallara told reporters, but added he thought this could be stabilised "once you get a new government in place, if that government reaffirms its intention to remain in the euro zone".

He was speaking on a visit to Ireland, which followed Greece into an international bailout in 2010 but has been far more successful in boosting exports to keep the economy afloat while slashing government spending.

Policymakers have begun to speak openly of the risk that Greece, now in its fifth year of recession, might leave the euro. Mr Dallara said the costs of a Greek exit would be so severe that Europe has to find a palatable way of solving their woes.

"I think that it (a Greek exit) is possible, but I wouldn't call it inevitable and I wouldn't even call it likely because the costs for Greece, for Europe and for the global economy are likely each in their own way to be immense," Mr Dallara said in a speech.

"The pressures on Spain, Portugal, even Italy and conceivably Ireland could be immense and the need for Europe to step up with much greater support for the banking systems would be substantial."