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ROME, Dec. 4 (Xinhua) -- Italians were expected to reject a proposed constitutional reform in a crucial referendum held on Sunday, exit polls showed.

The "No" vote would be between 54 percent and 58 percent, according to exit polls by Ipr-Piepoli Institute broadcast by Rai state television. The "Yes" vote would be between 42 percent and 46 percent.

Polling stations opened from 7 a.m. to 11 p.m. local time, and some 46.7 million Italians were eligible to cast their ballot. The turnout was 57.24 percent at 7 p.m., according to the Interior Ministry.

Over 3.9 million Italians living abroad had their chance to vote earlier this month.

Italians had to choose on whether confirm or reject a reform of the constitution that had already been passed by lawmakers earlier this year, but not with the required majority of two-thirds in each house of the parliament in the second vote.

The major amendment proposed was to cut the size of the senate to 100 from 315 seats, and strip it of the power to bring down the cabinet with no-confidence sessions, and vote on national legislation.

Currently, draft bills have to be approved by both houses in an identical text in order to become laws.

The referendum was also seen as a key test of popularity for Prime Minister Matteo Renzi's center-left cabinet.

The government has much advocated the reform, claiming it would help streamline the country's laborious law-making process, and increase the stability of the cabinets.

Italy has had more than 60 governments since 1948.

Opponents argued it would concentrate too much power in the cabinet, weakening the parliament's control.

Renzi has said he would resign in case of defeat, which might trigger a government's crisis and plunge the country back into a period of political and economic instability.

The vote has also been closely watched across Europe for a possible impact on the euro-zone.

The prime minister is expected to address the country around 12 p.m., local media said, citing government sources.