 "Greece's voters decide euro future in too-close-to-call poll")
Polling stations were open 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.
Read more from our special coverage on "GREECE CRISIS"
The European Union and international investors were intently watching the poll, which was the biggest challenge to the European single currency since it came into being in 1999 and was adopted by Greece two years later.
The outcome was far from certain. Polls suggest the 'Yes' and 'No' camps are neck-and-neck.
Prime Minister Alexis Tsipras insists a 'No' victory would strengthen his hand in negotiations with the country's international creditors. But EU leaders warn it would effectively be a vote to leave the 19-nation eurozone -- a so- called "Grexit".
Tsipras's flamboyant finance minister, Yanis Varoufakis, on Saturday accused Athens's creditors of "terrorism" for trying to sow fear around the vote. He has pointed out that no legal mechanism exists to force Greece out of what is meant to be an "irreversible" monetary union.
As the sun rose in a clear summer sky today, young and old were already queueing to have their say in schools and university buildings transformed into polling stations. Voting was to close at 7:00pm, with results expected hours later.
Dimitris Halatsis, a teacher, said it was "a crucial day" and he was voting 'No' because "it's the only chance the government and Greece have to apply pressure" on the creditors.
Michelis, an 80-year-old first through the doors of an elementary school being used for the vote on Skoufa street in central Athens, said he too was voting 'No' "because they'll take us more seriously".
In a room hung with children's drawings and maps he said that he was "not voting for myself, but for my grandchildren" and their future.
Theodora, 61, a retired journalist, said she was voting 'Yes' because "it's a 'Yes' to the European Union".
Tsipras, a radical leftist who came to power in January, has staked his political career on the plebiscite.
The 40-year old was to vote in an elementary school in central Athens, just north of the Acropolis.
His bombshell decision last week to put the issue to a referendum stunned international creditors, who accused him of ruining five-months of intense bailout negotiations.
In the largely middle-class Pangrati neighbourhood, voter turnout was high, with even the very elderly making their way determinedly up a flight of forty steps to reach polling booths set up inside a school.