The future of Italy's Prime Minister Matteo Renzi hangs in the balance as his country goes to the polls in a referendum on constitutional reform on Sunday (4 December).

The centre-left leader has promised to resign if the 'Yes' vote approving his initiatives to reduce the role of the upper house Senate and claw back power from regional authorities, fails.

Related: All you need to know about the upcoming referendum in Italy

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Polls opened at 7am local time (6am GMT), with 51 million Italians eligible to vote. However, many believe Renzi will be the next leader to be toppled in a year defined by populist sentiment.

With all opposition parties lined up against the reform, a victory for Renzi would be considered as a surprise and represent an enormous personal triumph for Italy's youngest prime minister, who often appeared to be fighting the campaign single-handedly.

"Think of your future and the future of your children," Renzi said on Italian radio, reported the Independent, in what was one of a number of media appearances throughout the day.

Though Italy banned the publication of surveys in the referendum from 18 November, many private bookmakers have carried out their own polls and say the 'No' camp is the clear favourite to win.

Bookmakers' odds suggest a roughly 75% of chance of the 'No' vote coming out on top however, voter turnout is expected to be crucial.

As Renzi's reforms are most strongly opposed by young voters and those in the poor south – segments of the population that often do not bother to vote – a low turnout would be beneficial for the 'Yes' vote.

A surprisingly high turnout would make the referendum vote far more unpredictable. If above 60%,, it would suggest many voters who said they planned to abstain ended up going to the polls.

The result of exit polls will be announced as soon as voting ends and the count begins at 11 pm (10pm GMT). After around 30 minutes, the first projections of the result will be announced on the basis of actual votes counted.

The winner could be revealed as soon as 1am (12am GMT). However, it is likely it will not to be known until 3am (2am GMT).