Italians were voting Sunday in a two-day referendum, of which the most important of four issues was whether to permanently abandon nuclear power production, DPA reported.
An estimated 47 million people were eligible to vote. With the validity of the referendum hinging on a quorum of a 50-per-cent-plus-one vote, several government ministers said last week that they would stay away and indicated their supporters should do the same.
The opposition leftists also see the anti-nuclear referendum as a plebiscite on controversial Prime Minister Silvio Berlusconi, and were happy about the strong turnout, which reached double-digit figures by noon.
Berlusconi - whose centre-right coalition received a drubbing in last month's local elections - has downplayed the significance of the vote.
The government has argued that the nuclear issue has been made redundant by a moratorium on nuclear power it introduced in April, a decision made in the wake of the damage caused by a March earthquake and tsunami to nuclear reactors in Japan.
But environmental activists and the centre-left called for a "yes" vote to uphold a ban on nuclear power introduced in a 1987 referendum held one year after the Chernobyl nuclear disaster in Ukraine.
Berlusconi has described the moratorium as a temporary freeze. He also says plans to build nuclear power stations would be put back on track once Italians have recovered from an "emotional response" to Fukushima.
The government says Italy - which has the highest energy bills in Europe - can ill-afford to continue depending on oil and gas imports to meet the needs of its economy, the eurozone's third-largest.
In addition to nuclear power, Italians are also voting on issues related to the privatization of water supplies and the validity of a law exempting top officials - including the premier - from attending trial when busy with government duties. The latter is especially important for Berlusconi who is currently involved in four trials.
The referendum continues Monday, with results expected later that day.
In Italy the last referendum to reach a quorum was in 1995. Since then six referendums have been declared void due to low turnout.