The moves came after an emergency eurozone leaders’ summit in Brussels.
European Council President Donald Tusk said this was now the “most critical moment in the history of the eurozone”.
The eurozone had expected Greece to submit fresh plans on Tuesday after its voters rejected a deal in a referendum, but no new proposals were tabled.
On Sunday, a meeting of all 28 members of the European Union will be held.
Mr Tusk said a Greek bankruptcy and the collapse of the Greek banking system would affect the whole of Europe, and that anyone who thought otherwise was naive.
“The final deadline ends this week,” he said.
French President Francois Hollande said: “It’s not just the problem of Greece – it’s the future of the European Union” that is at stake.
Greek PM Alexis Tsipras said he wanted a “socially just and economically viable agreement”.
“The process will be fast. It starts in the coming hours with the aim of concluding it by the end of the week, at the latest,” he said.
The new Greek proposals will be discussed by eurozone finance ministers on Saturday.
German Chancellor Angela Merkel said the eurozone leaders had had a “serious, candid discussion” in Brussels that “reflected the seriousness of the situation at hand”.
She said the leaders “obviously respect the results of the referendum” but added: “As regards the euro, we don’t have the sovereignty of just one country to contend with, but of 18. Shared sovereignty, shared responsibility.”
Mrs Merkel said Greece needed a new debt programme that would last several years, not a short-term fix.
European Commission President Jean-Claude Juncker said he wanted Greece to remain in the eurozone but that Greece had to “tell us where they are heading” by the end of the week.
Earlier there was anger among some eurozone members at the lack of new written proposals from Greece.
Lithuanian President Dalia Grybauskaite said: “There was a promise for today. Then, they’re promising for tomorrow. For the Greek government it’s every time ‘manana’.”
Greece’s banks have been shut since its last international bailout programme expired last Tuesday.
Capital controls have been imposed, with people unable to withdraw more than €60 a day from cash machines.
The European Central Bank (ECB) has refused to increase emergency lending.
However, Mr Hollande said on Tuesday the ECB would now ensure minimum liquidity for Greece until Sunday.