Emergency euro summit called on Greek No

He also said the question of Greece's debt sustainability - a red line for Athens and its euro partners - will "now be on the negotiation table".

The leftist leader, who ran a short but defiant campaign since his unexpected decision to call a referendum last Friday. said the result gives him "greater negotiating strength".

But the result puts the other euro states and the EU institutions in a quandry.

Berlin, Rome and the European Commission all said ahead of the vote that a No would mean a rejection of the euro or of Europe.

Martin Schulz, European Parliament president and one of the first top-ranking EU officials to give a reaction to the vote, said "we are in a very difficult situation".

"It is now up to the Greek government to make proposals so that it is possible and even effective to renegotiate".

If Athens does not do this, the eurozone will be "entering a very difficult and dramatic time".

Schulz added that the country should maybe receive humanitarian aid as old-age pensioners and young children "should not pay the price" for where Greece finds itself now.

His statements come as Greek banks remain closed and capital controls stay in place, amid reports of hardship on several fronts - pensioners having difficulty getting their money; businesses struggling to keep afloat; and hospitals concerned about medical supplies.

Meanwhile, although Tsipras says his bargaining hand has been strengthened by the vote, several euro countries' politicians were openly sceptical or hostile.

Slovak finance minister Peter Kazimir tweeted: "Rejection of reforms by Greece cannot mean that they will get the money easier" while German vice-chancellor Sigmar Gabriel said Tsipras had "torn down the last bridges on which Greece and Europe could have moved towards a compromise" and eurogroup chief Jeroen Dijsselbloem said the result was "very regrettable for the future of Greece".

Lithuanian president Dalia Grybauskaite said the situation had become "even more difficult" and Estonia's PM Taavi Rõivas referred to Tsipras' policies as "communism".

European Commission president Jean-Claude Juncker, for his part, said he would hold a conference call with the heads of the European Central Bank and eurogroup on Monday before addressing the European Parliament on the situation on Tuesday.

His brief written statement emphasized that he is consulting with "the democratically elected leaders of the other 18 eurozone members", with Tsipras having spent the last week emphasizing the importance of the democratic will of the Greek people.

On Monday evening, the French and German leaders will meet to discuss how to approach the situation.

While Germany has stuck to arguing that Greece must abide by the eurozone's legal rules, putting the emphasis on being a "responsible" member of the club, France in the last few days has emerged as Athens' most influential friend by taking a more emollient tone.