Greece's government says it may resign if Sunday night's referendum on the country's financial future goes against it.
And finance minister Yanis Varoufakis said he would not continue to serve as minister if Greeks vote to accept the conditions of an international bailout.
He was speaking as the International Monetary Fund (IMF) warned that Greece needs at least another €50bn to stabilise its finances.
"We really desperately want to stay in the euro even if we are critical of the institutional framework of the euro," Mr Varoufakis said.
Earlier, he told the ABC that the government "may very well" quit if the public went against it in Sunday's plebiscite and voted for more austerity in return for international bailout funds.
"We are on a war footing" to ensure the rushed referendum happens on time, Mr Varoufakis said.
The world's financial markets and Greece's creditors - the European Commission, European Central Bank (ECB) and International Monetary Fund (IMF) - are stepping back after days of dizzying drama to watch the outcome.
But European chiefs warned the situation was deteriorating and what could emerge after the vote remained unclear.
"The situation is only getting worse, due to the Greek government's behaviour," said Jeroen Dijsselbloem, Dutch finance minister and head of the Eurogroup of eurozone finance ministers.
"In case of a 'No', Greece's situation will become exceptionally difficult," he told Dutch politicians.
Such a result would plunge Greece and the eurozone "into the unknown", French president Francois Hollande said on an African visit.
Ordinary Greeks are divided over which way to vote and even what the referendum is about.
The Greek government led by prime minister Alexis Tsipras believes rejecting the bailout conditions would strengthen its hand in negotiations with creditors.
Orange posters urging a 'No' vote line Athens streets, the word 'OXI' (no in Greek) stamped in large black letters.
But support for the 'No' camp sharply slid this week as Greeks struggled under capital controls reducing ATM withdrawals to €60 a day.
The government's failure on Tuesday to make a €1.5 billion loan repayment to the IMF has also focused minds.
Athens is now in danger of falling in arrears to the ECB if it also fails to pay €3.5 billion on July 20.
Mr Tsipras's call for a 'No' has split the ruling coalition, with members of partner party Independent Greeks rebelling.
One of its politicians, Constantin Damavolitis, was expelled from the coalition benches for calling for a 'Yes' vote.
"The day after the referendum, we will be united," Mr Tsipras promised in a quick briefing to journalists after meeting Independent Greeks party chief Panos Kammenos, who is defence minister.
But Mr Varoufakis told the ABC that a 'Yes' result could see the government handing over to a caretaker administration.
"Yes, we may very well do that. But we will do this in the spirit of cooperation with whoever takes over from us," he said.