Italians voted yesterday overwhelmingly to elect Matteo Renzi as the new head of the ruling Democratic Party, returning him to frontline politics as the party faces a growing challenge from populist politicians.

"It is a clear, ample victory that went beyond our expectations," said agriculture minister Maurizio Martina, who has been campaigning for Mr Renzi. "This is the opening of a new phase."

Voters queued at tents, bars and local party headquarters across the country to choose between Andrea Orlando, the justice minister, Michele Emiliano, governor of the southern Puglia region, and Mr Renzi, the former prime minister.

Turnout was estimated at between 1.9 to 2 million voters, an "extraordinary" result, said Mr Renzi, 42, who resigned in December after Italians overwhelmingly rejected a national referendum to reform Italy’s constitution.

In remarks on the terrace of the party headquarters, Mr Renzi said the primary victory - estimated to be well over 60 percent - marked the "turning of a new page" for the party, and possibly the future of Europe.