Some 13 million Italians, nearly a quarter of the population, are eligible to vote in 1,310 towns and provinces, although turnout is expected to be relatively low because of disillusionment with the stormy political climate.

The most important contests are in the four big cities of Turin, Naples, Bologna and Milan -- Italy's business capital and Berlusconi's home town, where his center-right coalition runs the risk of losing for the first time in nearly 20 years.

The local vote, which runs through Monday, follows opinion polls putting Berlusconi's popularity at about 30 percent, the lowest since he swept to power for the third time in 2008.

But more than once in the past the 74-year old premier has defied predictions that his grip on power was weakening.

"The problem is that when people are inside the polling station, they change their mind and always end up voting for Berlusconi, and that is because the center left does not have a leader as strong as him in terms of charisma," said Milan resident Giorgio Cecchi.

Since March, Berlusconi has faced four concurrent trials for corruption, tax fraud and, most sensationally, having sex with an underage prostitute and then using his office to cover it up.

Berlusconi denies all charges and says Milan magistrates are politically biased leftists bent on destroying him.

He is also battling accusations that he has failed to tackle Italy's low growth, and strains have intensified in his alliance with the pro-devolution, anti-immigrant Northern League.

Data on Friday showed Italy's economy grew just 0.1 percent in the first quarter, far below Germany's 1.5 percent growth but also lagging the 0.8 percent expansion of debt-stricken Greece.

The League, vital for Berlusconi's survival after he split from long-time ally Gianfranco Fini, has repeatedly distanced itself from him, notably opposing Italy's involvement in the NATO bombing of Libya.