ROME - Italians started to cast their ballots Sunday morning leading to the election of a prime minister, two days after politicians made their final campaign for the general election.

The voters have to choose among three main forces: the populist Five Star Movement, a center-right coalition led by media mogul and former Prime Minister Silvio Berlusconi, and the center-left Democratic Party of outgoing Prime Minister Paolo Gentiloni.

Further on the left is the smaller Free and Equal (LeU) party led by Senate Speaker Pietro Grasso and made up of defectors from the Democratic Party. There is also a plethora of smaller parties, ranging from the far left to the extreme right.

In terms of opinion polls, Berlusconi's alliance is the front-runner. The media mogul, who is barred from public office until 2019 following a tax fraud conviction, has promised to expel 600,000 immigrants from Italy and to introduce a 23 percent flat tax, in a country where the tax burden is over 40 percent for both individuals and businesses.

However, his coalition is seen as shaky, mainly because its two rightwing partners are protectionist on trade and anti-European Union (EU), while Berlusconi's Forza Italia party is pro-EU and supports free trade.

Second in opinion polls is the anti-establishment Five Star Movement, which has always spurned entering into alliances with other parties, claiming they are all corrupt. Their program calls for a crackdown on immigration, guaranteed universal income, and defying EU rules on public spending.

The Five Star Movement has in the past espoused no-tax and anti-EU positions -- much like Italy's far-right anti-immigrant League party, which is running in an alliance with Berlusconi's Forza Italia party -- but its leader, Luigi Di Maio, has taken pains to distance himself from such positions.

The pro-EU Democratic Party led by former Prime Minister Matteo Renzi is polling third. It has ruled over the past five years, pushing through controversial reforms which have proved unpopular on the domestic front, but have also been credited with pulling Italy out of its longest postwar recession and sparking the country's sluggish recovery.

The Democratic Party supports free trade, moderate public spending, and managing immigration rather than shutting down borders -- an unpopular view right now, as voters appear to have swung to the right in response to the entry of the hundreds of thousands of African migrants who have reached Italy in the past five years.

Italians are being called on to choose their representatives in the 315-member Senate and the 630-seat Lower House under a new electoral law that is one-third majority and two-thirds proportional -- meaning that no single party or coalition is likely to win enough seats to claim an absolute majority.

This means that after Sunday's vote, the different political forces will have to work together to reach a compromise.

This may be a tough call, as most of the major players have taken pains to assure their potential voters that they will never make deals with parties whose views differ radically from their own.

Some analysts here believe that the voting is one of the most uncertain elections in years and might determine if Italy would succumb to the populist, Euroskeptic and far-right sentiment that has spread Europe-wide.

The voting ends late afternoon and the final result was expected to come out late Sunday night.