Across the country of 11 million people -- on far-flung Aegean islands, in the shadow of the 2,400-year-old Parthenon in Athens, to the northern border shared with fellow EU state Bulgaria -- voters were set to cast their ballots.
The rest of Europe, and international investors, will be watching intently, unsure of the outcome that could greet them tomorrow. Polls suggest both the 'Yes' and 'No' camps are neck-and-neck.
He announced it a week ago in a bid to break a five-month impasse with international creditors and insists a 'No' vote would force a restructuring of Greece's massive debt and a softening of drastic austerity conditions.
But many who first backed him have swung to the 'Yes' camp, heeding warnings from EU leaders, notably European Commission chief Jean-Claude Juncker, that a 'No' result could see Greece expelled from the 19-nation eurozone -- a so-called "Grexit".
Tsipras's flamboyant finance minister, Yanis Varoufakis, yesterday accused Athens's creditors of "terrorism" for trying to sow fear around the vote.
He pointed out that no legal mechanism exists to force Greece out of what is meant to be an "irreversible" monetary union.
Greeks were nevertheless alarmed this week when the government imposed capital controls, closing banks and limiting daily ATM withdrawals to just 60 euros (USD 67), to stem a bank run.
