MILAN (AP) — Italians vote Sunday in a referendum on constitutional reforms that is being closely watched abroad to see if Italy becomes the next country to reject the political status quo.

Premier Matteo Renzi has said he will resign if the reforms are rejected, and opposition politicians have vowed to press for a new government if voters reject the proposed constitutional changes.

The premier made no comment as he voted in Pontassieve, a Tuscan town east of Florence, along with his wife, Agnese Landini. He is expected to return to Rome later this afternoon to watch the outcome of the vote.

The risk of political instability in Italy, Europe's fourth largest economy, has triggered market reaction before the vote, with bank stocks sinking and the borrowing costs on sovereign debt rising.

European partners were closely monitoring the vote, which comes on the same day as a runoff in Austria that could put a right-wing populist in power for the first time since World War II.

A headline in the Frankfurter Allgemeine Zeitung said Renzi's "arrogance is his shortcoming," noting that "Europe is at stake" in the vote. The Guardian noted that the referendum was among a series of votes in Europe that could "conceivably herald the end of the European project in its current form."

The referendum aims to streamline Italy's cumbersome lawmaking process by reducing the powers of the Senate, while also removing some key decision-making powers from regions.

Renzi has argued that the reforms dismantle bureaucracy and will make Italy more attractive to investors and help his drive to transform the country. But his decision to tie the outcome to this political future transformed the vote into a plebiscite on his leadership.

Political opponents are hoping to tap populist sentiment that has been gaining ground with the U.K. vote in June to leave the European Union and the U.S. presidential victory by billionaire political outsider Donald Trump.

A "yes" vote would strengthen Renzi's 2 ½-year-old government, giving it impetus to complete its five-year term and time to prepare for elections in 2018, while a "no" vote would favor early elections sometime next year.

Three former premiers — Silvio Berlusconi, Massimo D'Alema and Mario Monti — have come out against the reform, albeit for different reasons. Berlusconi has argued that it concentrates too much power in the premier, while Monti says the reforms don't go far enough and downplayed the risk of political instability.

How the vote plays out politically is likely to depend on the turnout and the margin of the decision.

"For example, if only 30 percent of eligible voters turn out, the result will hardly be influential," the founder of La Repubblica, Eugenio Scalfari, wrote in a column on Sunday.

If voters reject the referendum, Renzi is expected to announce his resignation right away. But analysts say President Sergio Mattarella, whose job it would be to designate someone to form a new government, is unlikely to move until parliament passes a new budget law.

More than 46 million Italians were eligible to cast votes from 7 a.m. until 11 p.m. (0600 GMT until 2200 GMT) while another 4 million were registered to vote abroad. The overseas votes were being tallied under guard at a warehouse outside of Rome.