Italian President Giorgio Napolitano on Tuesday called for political mainstream parties to think over the significant protest vote registered in local elections.

"Causes for reflection have emerged from the vote for parties and citizens about the relationship between the political world and the governability problems at the local level," Napolitano was quoted as saying by local media.

Candidates supported by leftist coalitions appeared to be the favorite choice for over 6 million voters in nearly 1,000 municipalities, while the center-right People of Freedom (PdL) party of former Prime Minister Silvio Berlusconi suffered the strongest setback.

Grassroots Five-star Movement led by comedian Beppe Grillo, which openly opposes mainstream politicians, captured a significant share of the votes in various big towns including Parma in central Italy and Genoa in the north.

The outcome was especially seen as a backlash against mainstream political leaders who supported a recent tough program of austerity reforms, including pension cuts and tax hikes, amid escalating corruption scandals within their parties.

"This was a historical date, about which I feel a big responsibility as citizens' eyes will be now directed towards us," 32-year-old Roberto Castiglion, the first-elected mayor from the Five-star Movement in northern Veneto region, was quoted as saying by Sky television.

"Common citizens have voted themselves, marking a momentous change in the political thinking, and this was only the beginning of regeneration Napolitano was calling for," Grillo said.

However, Napolitano played down the importance of the boom of votes registered by the movement defending the established parties against "anti-politics," while Interior Minister Anna Maria Cancellieri pointed out that "local elections did not concern the government."

Pier Luigi Bersani, secretary of center-left Democratic Party (PD), one of the three main political forces supporting Prime Minister Mario Monti's cabinet of technocrats, denied that all parties were losers.

"Results of PD were good everywhere ... Voters have understood our support to Monti's government," he claimed.

But Angelino Alfano and Pier Ferdinando Casini, leaders of the other two groups supporting the emergency cabinet PdL and centrist Third Pole acknowledged Italians' discontent.

"Mainstream parties have been defeated ... It is now necessary to seriously reflect as there is great concern about the overall picture emerging from the vote," Casini said.