The Greek government has extended bank closures and a €60 (£43; $66) daily limit on ATM withdrawals until Monday.
The curbs were imposed on 28 June, after a deadlock in bailout talks with creditors led a rush of withdrawals.
The European Central Bank has decided not to increase support for Greek banks until the debt crisis is resolved.
Greek PM Alexis Tsipras says he will submit “credible” reform plans on Thursday – ahead of a Sunday deadline by the EU to find a solution.
An emergency summit will involve all 28 EU members – not just the 19 eurozone countries.
European Council President Donald Tusk has warned that this was now the “most critical moment in the history of the eurozone”.
“The final deadline ends this week,” he said after emergency talks of the eurozone leaders in Brussels on Tuesday.
Greece is desperate for a third bailout to avoid bankruptcy and possibly crashing out of the euro currency.
“The bank holiday is extended to July 13,” the finance ministry said in a statement late on Wednesday.
The announcement came after the European Central Bank – which has been providing emergency liquidity to keep Greek banks from collapsing – said it would leave its current level of support unchanged.
Greece’s last international bailout programme expired on 30 June and it missed an International Monetary Fund (IMF) payment.
Mr Tsipras, speaking during a fractious debate on the Greek debt crisis in the European Parliament on Wednesday, criticised previous bailouts for turning Greece into an “austerity laboratory”.
He was speaking after the Greek people decisively rejected the latest proposals from creditors in Sunday’s referendum.
In an address in Washington on Wednesday, IMF Managing Director Christine Lagarde reiterated that debt restructuring alongside a programme of reforms was the only way forward for the stricken Greek economy.
“Greece is in a situation of acute crisis, which needs to be addressed seriously and promptly,” she said.
Meanwhile, the Greek government has insisted that there is no threat to food and fuel supplies.
In a statement, the Ministry of Economy, Infrastructures, Maritime Affairs and Tourism “reassures both the Greek citizens and the visitors (tourists) that there are adequate food supplies in the market and that their prices remain stable”.
Greece’s creditors – the European Commission, the European Central Bank and the International Monetary Fund – have already provided more than €200bn in two bailouts since a rescue plan began five years ago.
Sources say Athens is requesting a fresh three-year loan in exchange for reforms.