Florence Mayor Matteo Renzi on Sunday is leading with a large majority of votes in a primary against his rivals to choose the secretary of Italy's ruling center-left Democratic Party (PD).

With 6,625 of the 8,476 polling places reporting, Renzi had around 68 percent of votes to 18 percent for Gianni Cuperlo and 14 percent for Giuseppe Civati.

The primary had a turnout of around 2.5 millions of party and non-party voters, anyone over 16 who is Italian or resident in Italy regularly, according to party sources.

In his electoral campaign, the charismatic 38-year-old insisted on the need to put aside the senescent Italian politicians and give green light to deserving newcomers.

Renzi, who was defeated by former PD secretary Pier Luigi Bersani in the party's previous primary last year, said he would try to give birth to a new vision of politics based on merit, innovation and quality.

The Florence mayor hailed the victory, saying he was "proud" of the so many electors who despite the ongoing difficult times decided to believe in the possible "change" of Italian politics.

"The moment has come for a new generation," Renzi said, promising he and his group will try their best to relaunch Italy and value its many hidden excellences.

"Italy needs us," he said, calling Italy's political class "the worst that Europe's history has known in the past 30 years."

Renzi, whose modernizing campaign had triggered many angry reactions, said his victory was not the "end of Italy's left" but the "replacement of a group of players who have done their best but need now to be substituted."

The PD of Prime Minister Enrico Letta has a narrower but more cohesive government coalition with a group of center-right moderates who split from former premier Silvio Berlusconi's party.

Analysts said Renzi has what it takes to defeat the center-right in the next national election, which is widely expected at the beginning of 2015.

Earlier this week, Renzi said he was disappointed that the Letta government was "delaying things."

Renzi added he will back the ruling coalition if it moves swiftly to enact much-needed structural reforms, but many observers argue he might try to bring the government down if it does not do so.