Mr Berlusconi, voting in Milan, referred to the tensions in Italian politics
Turnout is reported to be low on the first day of Italian regional elections seen as a major test for Prime Minister Silvio Berlusconi.
Thirteen out of 20 regions are involved in the vote, which is being held over two days.
Mr Berlusconi has been at the centre of a series of political and personal controversies, which may affect the chances of his People of Freedom party.
Analysts say a low turnout could favour opposition parties.
By 1900 local time (1700 GMT) on Sunday turnout was down seven percentage points, at 35%, from the same time in the last regional elections in 2005, officials said.
"The only possible way to read these first numbers is that turnout will be 10 points below five years ago, at 62% or maximum 65%," said pollster Nicola Piepoli, quoted by Ansa news agency.
The BBC's Duncan Kennedy in Rome says that after the European Parliament elections last June, the regional elections on Sunday and Monday represent the biggest test of public opinion since Mr Berlusconi was re-elected in 2008.
Mr Berlusconi, who campaigned for his People of Freedom (PDL) party on the slogan "Love Always Wins Over Envy and Hatred", has seen his approval rating slip.
As he cast his vote in Milan, Mr Berlusconi kept with the theme, saying: "I hope hatred will not win out over love."
Some 41 million Italians are eligible to vote - two-thirds of the population.
Close contests are expected in Lazio, which includes the capital, and Piedmont, an affluent northern region held by the centre-left.
December: Hit in the face with a model cathedral in Milan, breaking two teeth and fracturing nose
October: Court overturns law granting PM immunity from prosecution while in office
July: Media release audio recordings allegedly of night he spent with an escort; admits "I'm no saint" but denies paying for sex
June: Forced to deny allegations he had paid prostitutes to attend parties at his official residences
June: Photos published showing topless women and a naked man at his villa in Sardinia and of celebrity using PM's official jet
May: Wife announces she is divorcing him after he attends the 18th birthday of "female friend"
April 2009: Tells victims of earthquake they should pretend they are on a "camping weekend"
The PDL currently controls only two of the 13 regions at stake, but had been expected to pick up more this time, our correspondent says.
However, a series of political and personal controversies surrounding Mr Berlusconi in recent months could limit the gains, he adds.
The party's candidates have been barred from standing in Lazio after an official missed a deadline to submit the required documents.
The government passed an emergency decree to ensure the electoral list was included, but a top court overturned it.
A corruption investigation into building contracts for last year's G8 summit in the earthquake-stricken Italian city of L'Aquila has also implicated Mr Berlusconi's civil protection chief, Guido Bertolaso.
Then last week, Italian media said the prime minister was being investigated for allegedly trying to pressure the communications watchdog to block state TV talk shows critical of his government.
Mr Berlusconi had already suffered a turbulent 2009, marked by allegations about his friendship with a teenage model and about escort girls attending parties at his residences.
His wife also filed for divorce, and he suffered a broken nose when a man threw a model of Milan cathedral at his face.
Unemployment and the economy are also concerns for voters.
Some analysts say a poor result in the regional elections for the PDL might give the Northern League more power over Mr Berlusconi in the coalition government.
Others say the 73-year-old billionaire may even face a challenge to his leadership - possibly from the president of the Chamber of Deputies, Gianfranco Fini - though that is seen by most as unlikely.
Our correspondent says the regional elections a rare chance for millions of Italians to express their views on Mr Berlusconi.
Although turnout may not be high, the results will be studied by his allies and opponents alike, to see which direction Italy will follow, he adds.
Earlier, police said the postal service had intercepted a letter addressed to Mr Berlusconi containing a bullet.
A package, directed at a party in Mr Berlusconi's coalition, the Northern League, was also seized but exploded, slightly injuring a postman in Milan.
A note in the package named the Interior Minister, Roberto Maroni, who has introduced tougher laws on illegal immigration. An anarchist group said it had sent it.