Prime Minister Silvio Berlusconi headed for a heavy defeat on Monday in four referendums after Italians turned out in large numbers for a vote he had urged them to boycott.

The proposals to repeal Berlusconi-era legislation on nuclear power, water privatisation and trial immunity for government ministers had been opposed by the prime minister, who declared that he would not cast a vote.

The referendums needed a quorum of more than 50 percent to be valid and looked set to meet the target easily. With supporters of the proposals considered far more likely to turn out to vote, they are expected to pass overwhelmingly.

According to figures from the Interior Ministry, turnout was running at 57 percent with some 98 percent of the vote counted, a huge turnaround from the lacklustre participation in previous referendums.

Berlusconi, facing mounting problems since heavy local election losses last month, appeared to concede defeat at least in the nuclear referendum when he told a news conference the vote had probably ended prospects for atomic energy in Italy.

"Following the decision the Italian people are taking at this moment, we must probably say goodbye to the possibility of nuclear power stations and we must strongly commit ourselves to renewable energy," he said.

The vote could not have come at a worse time for the 74-year-old premier, who faces a sex scandal and three fraud trials and who was weakened by crushing losses in last month's local elections, including in his northern power base, Milan.

The centre-left opposition campaigned hard to get voters to the polling stations. The last referendum to reach a quorum was in 1995. Six have been declared void since then.

After what he called "an extraordinary day," Pierluigi Bersani, leader of the centre-left Democratic Party, called for Berlusconi to resign.

"The government and Berlusconi really have to reflect on this. After the local elections and now the referendums, it would be irresponsible for them not to," he said.