Italians voted Sunday in regional elections seen as a key measure of the fading fortunes of ex-premier Silvio Berlusconi as well as an important test for centre-left Prime Minister Matteo Renzi.

Twenty million voters are eligible to elect governors in seven of the country's 20 regions, as well as the mayors of more than 700 municipalities.

By 7:00 pm (1700 GMT), 12 hours after polls opened, turnout stood at nearly 50 percent in the municipal polls and between 34 and 42 percent in the regional balloting.

The polls are the first in Italy, which is slowly emerging from recession, since European elections a year ago in which Renzi's Democratic Party (PD) won with just over 40 percent of the vote.

Observers will also be looking closely at the battle on the right between the anti-immigration Northern League, led by rising star Matteo Salvini, and Berlusconi's Forza Italia (Go Italy).

The 78-year-old media magnate is keen on making a political comeback after his acquittal on charges of paying for underage sex and a stint of community service for tax fraud.

Thirty elected members of Forza Italia have already announced their departure to join the man once considered Berlusconi's heir apparent, Raffaele Fitto, who has broken away from the old leader.

Berlusconi caused a stir on Friday when he swept into a leftist election rally flanked by six bodyguards, believing that he was at a Forza Italia event.

He beat a hasty retreat after being informed of his mistake by a member of his entourage in an embarrassment that the La Stampa daily on Sunday called "tragi-comic".

A key test for Renzi will come in the northern region of Liguria, where the PD's candidate faces rivals in both a left-wing dissident and the right-wing Giovanni Toti, supported by both the Northern League and Forza Italia.

At present, five of the seven regions holding elections are governed by the left, one is led by the League and another by Forza Italia.

In Campania in the south, the PD's candidate Vincenzo De Luca, fighting the Forza Italia incumbent, has been named in a list of 17 "unpresentable" candidates by an anti-mafia commission.

De Luca has a conviction for abuse of power and faces trial on other charges, including fraud, and could be banned from taking office.

Although an embarrassment for Renzi, the 40-year-old premier's popularity appears to remain high after nearly a year-and-a-half at the helm.

Polls were to close at 11:00 pm, with the first results expected on Monday. In Sicily, voting will extend into Monday.