Italians are heading to the polls in a referendum which could have significant ramifications for the whole of Europe.

The public are being asked to vote 'yes' or 'no' to constitutional change which would reduce the power of the Italian senate in order to streamline Italy's notoriously gridlocked legislative process.

By 7pm (local time) more than 57% of Italians had gone to their polling stations, the Interior Ministry said.

On the face of it, it's dry domestic politics which, while important for Italy, wouldn't normally prick much interest beyond the country.

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However, Prime Minister Matteo Renzi, who called the referendum and wants the change to be voted for, has staked his political career on winning.

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If the vote is 'no', he has pledged to resign; a promise he made when the polls suggested he'd win by a margin.

Now the polls are neck and neck. If he sticks to his resignation pledge, it could plunge the country into political turmoil.

That in turn would cause economic instability in a struggling eurozone country.

And so at the EU headquarters in Brussels, the eurozone headquarters in Frankfurt and in capitals across the continent they're watching anxiously.

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Prime Minister Renzi's promise to go has, for many voters, turned the poll into a referendum on his leadership.

Prominent populist opposition parties have pushed for a 'no' vote to force Mr Renzi from office.

On the far right of politics and powerful in the north of the country, the Lega Nord, or Northern League, is led by Matteo Salvini.

Image: Shadows are cast against the Italian flag under a stage with words reading 'I say no'

An MEP in the European Parliament, Mr Salvini's popularity as the party leader has been boosted by his anti-immigration views and pledges to federalise the country.

At the other end of the spectrum, The Five Star Movement is more of a threat to the centrist government led by Mr Renzi.

Led by comedian Beppe Grillo, it is populist, anti-establishment and now counts the powerful mayors of Rome and Turin among its number.

And so, in a now globally familiar way, the referendum has become about knocking out the establishment. Consequently the motivation to vote - either way - is huge.

In the ancient Tuscan town of Siena we found the referendum was exercising minds.

This is a place that would feel the consequences of the economic turmoil which a Renzi resignation could cause.

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"The economic difficulties we have faced? No one has been able to avoid them," Stefanio Osti tells me.

Mr Osti is the General Secretary of the local football club.

Until 2011, Robur Siena were in the top league of Italian football. Then their main backer and sponsor, the local struggling bank, pulled out. The club went bankrupt.

"Everything is so connected to the bank that whatever happens to the bank happens to us," Mr Osti says.

That principle of interconnectivity applies at a much larger level too, between Italy and Europe.

The football club's troubled bank, which happens to be the world's oldest, is Monti Dei Paschi di Siena.

Founded in 1472 it has been lending for 544 years. Now its balance sheet is in tatters.

With political instability, the uncertainty hanging over the Monti Dei Paschi would increase and it's not alone.

Unicredit is Italy's largest lender. It has 20 billion euros of bad debts and it owns a large German bank.

Eurozone banks are intertwined and vulnerable. The continental strain of an Italian banking collapse would be huge.

The University in Siena is even older than the bank. Pierangelo Isernia runs the department of political science.

"The problem is that when you have multiple crisis facing you at the same time, from very different angles, you are in trouble," he tells me.

"We have at least three crises going on in Europe. One: financial and economic. Another: the refugee and immigration crisis and last but not least, the security crisis, because most of what is going on in terms of civil wars is taking place at our borders; Syria, Libya."

Addressing public angst, anti-establishment political parties are capitalising on the multiple stresses.

Italy is deeply affected by all three of the crises the professor lists. That's motivating the decisions Italians are taking this weekend. The direction they chose could be critical to the continents stability.

"Can Europe face all these crises at the same time? Hard to know but that's why I am worried," Professor Isernia says.