Alexis Tsipras

In a joint letter to the government Wednesday, five associations urge Prime Minister Alexis Tsipras not to risk the country's place in the euro.

Overcoming their surprise when Tsipras failed to present them with a detailed plan, the leaders reluctantly agreed to a final summit Sunday, saying that could give both sides an opportunity to stave off collapse of the struggling but defiant member nation.

Underscoring the gravity of the challenge, European Union President Donald Tusk decided to call all 28 EU leaders to Brussels instead of only the 19 eurozone members, because, for the bloc, it "is maybe the most critical moment in our history."

With Greece's banks just days away from a potential collapse that could drag the country out of the euro, Tsipras had been expected to offer up economic reforms in exchange for loans.

Instead he came with only vague proposals and a commitment to back it up with real figures and a written plan on Wednesday.

"You know, there was a promise for today. Then, they're promising for tomorrow," said Lithuanian President Dalia Grybauskaite. "For the Greek government it's every time 'manana.'"

Cuban state media are carrying the text of a letter he wrote to Tsipras.

In a meeting with Pavlopoulos, Tsipras was expected to have presented his plans for negotiating a new bailout deal with the country's creditors.

Pavlopoulos says he accepted Tsipras' demand, saying that the referendum was not about staying in or leaving the euro.

Meanwhile, Police say about 100-150 anarchist protesters have started throwing firebombs at riot police and setting trash cans on fire in the central Athens neighbourhood of Exarcheia. This is far from the place where celebrations are taking place by supporters of the "no" vote in Sunday's referendum.

Early indications suggested a high turnout after a week of intense campaigning left Greek cities littered with fliers and posters — and opinion polls showed voters evenly split on the first referendum Greece has held in 41 years.

Prime Minister Alexis Tsipras, who was gambling the future of his 5-month-old left-wing government on the hastily called poll, insisted that a "no" vote would strengthen his hand to negotiate a better deal with creditors while a "yes" result would mean capitulating to their harsh demands.

Greece has agreed to reforms that are very close to what creditors have demanded before they release new loans, officials said on condition of anonymity because of the sensitivity of the negotiations. 

The creditors in return offered Greece a five-month extension to its bailout program, which was supposed to end Tuesday.

The concessions come only days after Greece proposed 8 billion euros in budget savings over two years. 

Before the finance ministers' short meeting, Greek Prime Minister Alexis Tsipras had held long talks with key creditors but apparently failed to reach a compromise over what kind of reforms the country should make in return for much-needed loans.

Greece has promised mainly tax increases to achieve budget savings, whereas the International Monetary Fund would like more spending cuts. Tsipras rejected the creditors' suggestions.