Prime Minister Alexis Tsipras says the “next hours will be crucial”.
His cabinet is meeting to discuss the plans which need to be submitted to Greece’s creditors by 22:00 GMT on Thursday.
The new proposals will be studied by eurozonefinance ministers on Saturday and a full EU summit on Sunday.
The Greek government has meanwhile extended bank closures and the €60 (£43; $66) daily limit on cash machine withdrawals until Monday.
The curbs were imposed on 28 June, after a deadlock in bailout talks with creditors led to a rush of withdrawals.
Louka Katseli, the head of the Greek bank association, said on Thursday that there was enough liquidity in cash machines to serve the public until Monday.
The German Chancellor Angela Merkel said that “a classic haircut” (meaning reducing the value of Greece’s debts) was “out of the question” for her.
Speaking in Sarajevo, Mrs Merkel described Sunday’s EU summit as a decisive and important meeting.
“We must not forget that the Greek people are suffering at the moment,” she said.
Thursday 9 July: 22:00 GMT deadline for Greece to submit new proposals.
Friday 10 July: ECB, EU and IMF discuss proposals at technical level.
Saturday 11 July: Eurozone finance ministers discuss plans (Brussels 13:00 GMT).
Sunday 12 July: Eurogroup leaders meet (14:00 GMT) followed by summit of all 28 members of the European Union (16:00 GMT). Both Brussels
Monday 20 July: €3bn payment due from Greece to the European Central Bank.
Mr Tsipras returned to Athens on Wednesday night after meetings in Brussels and an address to the European Parliament.
He has pledged to submit “new concrete proposals, credible reforms, for a fair and viable solution” by the end of Thursday. However, the details are scant.
This would be a fresh loan “to meet Greece’s debt obligations and to ensure stability of the financial system”, Greece says.
In return it has suggested it will implement new pension and tax measures from Monday.
French PM Manuel Valls said this was a step in the right direction.
And Christine Lagarde, managing director of the International Monetary Fund (IMF), one of Greece’s creditors, on Wednesday admitted that “[restructuring] is needed in the case of Greece for it to have debt sustainability”.
She said: “Greece is in a situation of acute crisis, which needs to be addressed seriously and promptly.”
On Thursday, EU Economics Commissioner Pierre Moscovici said he was hopeful of a new deal: “I have the sense that the dialogue is established, or restored, and that there is a way out.”
Mr Tusk tweeted: “Realistic proposal from Athens needs to be matched by realistic proposal from creditors on debt sustainability to create win-win situation.”
Greece’s creditors – the European Commission, the European Central Bank and the IMF – have already provided more than €200bn in two bailouts since a rescue plan began five years ago.
The second bailout expired on 30 June.
The creditors had hoped for new, concrete proposals from Greece at a meeting on Tuesday but these were not submitted and they instead agreed to set a new deadline of Thursday.
Greece has been warned this is the “final deadline”.
Mr Tusk has said this is “now maybe the most critical moment in the history of the eurozone”.
“This is really and truly the final wake-up call for Greece and for us, our last chance,” he said, adding that failure “may lead to the bankruptcy of Greece”.
Mr Tsipras’s Syriza party was elected in January pledging to oppose the harsh austerity measures demanded by creditors.
And on Sunday, the Greek people decisively rejected the latest bailout proposals from creditors in a referendum.
Energy minister and influential Syriza member Panayiotis Lafazanis insisted on Thursday that Greece would not sign up to a third bailout if it brought “harsh austerity, suffering and deprivation to the Greek people”.
He insisted Greece had “alternative options to a new bailout deal” and there was “no gun pointed at its head”.