British prime minister David Cameron has called on eurozone leaders to either back the group's weaker economies or kick them out altogether.

Mr Cameron has declared Europe is at a crossroads, saying leaders can choose between a "stable, successful eurozone or uncharted territory that carries huge risks for everybody".

The British prime minister says the weaker nations, which includes countries such as Greece, Spain, Italy and Portugal, are less likely to sustain the "necessary adjustment economically or politically" unless support for them is bolstered.

"The idea that high-deficit countries can borrow and spend their way to recovery is a dangerous delusion," he said.

Mr Cameron is just one of a host the European leaders worried about Greece's future in the single economic bloc. European Commission president Jose Manuel Barroso has called for Greeks to choose wisely in the upcoming elections.

But enraged with repeated rounds of austerity that have slashed wages and sent jobless rates soaring, Greek voters have rallied around leftist party Syriza, whose charismatic leader Alexis Tsipras has promised to tear up the bailout deal.

Mr Tsipras, 37, has predicted his party will sweep next month's election, and has once again demanded an end to the "barbaric" austerity policies he says are bankrupting the nation.

The latest poll, conducted for the To Pontiki newspaper on May 15-16, backs up that prediction, showing Syriza taking 24.5 per cent of the vote in the election, putting it ahead of all other parties.

First place, which comes with a bonus of 50 extra seats in the 300-seat parliament, went to the conservatives in the election earlier this month.

Mr Tsipras predicted the mood among voters would not change leading into the elections and predicted Syriza would have twice as many politicans in power in a month's time.

"The Greek people voted for an end to the bailout and barbaric austerity. They ignored the threats and the cheap propaganda. And we are certain they will do the same now," he said.

"The people will complete on June 17 the great step forward they took on May 6, regardless of what (EC president) Mr Barroso says.

"They are trying to terrorise the people to make Syriza cave in. We will never compromise.

"We will never participate in a government to rescue the bailout."

'Extremely expensive'

Greece's long-running economic crisis turned into a full political crisis after the parties opposed to the terms of a 130-billion-euro ($168 billion) bailout made strong gains in the May 6 vote, leaving the country without a government and raising the odds that it would renege on terms of the deal.

Earlier this week, the country's president said Greeks had withdrawn up to 800 million euros ($1 billion) from banks as the political uncertainty deepened. In a further blow, the European Central Bank said it had halted liquidity operations with some Greek banks because their capital was too depleted.

Fears that Greece's dire state could drag the eurozone deeper into crisis kept markets on edge across the world on Thursday, and IMF chief Christine Lagarde warned of "extremely expensive" consequences if Greece were to leave the eurozone.

An emergency government led by a judge and made up mainly of professors, technocrats and a few politicians that will lead the nation to next month's election was sworn in on Thursday in a ceremony.

Caretaker prime minister Panagiotis Pikrammenos's cabinet includes senior finance ministry official George Zanias as the new finance minister and Petros Moliviatis, a former conservative minister, who has the foreign affairs portfolio.

As Greece's chief economic adviser, Mr Zanias has participated in meetings of eurozone finance ministers and was involved in negotiating the bailout and a debt restructuring.

At his first cabinet meeting, Mr Pikrammenos told the ministers they would receive no salary for their month in office and urged them to dispense with frills like limousines or business trips, saying they should not be an additional burden for the country.

Reuters