Former prime minister Silvio Berlusconi and fellow leaders of his centre-right alliance made their first, and only, joint appearance on Thursday in an effort to project an image of unity ahead of Sunday's election.

Before a blackout was imposed on new opinion polls two weeks ago, the centre-right alliance was seen winning around 36 percent of the vote, a score that would give it more seats than any other bloc, but falling short of an absolute majority.

Italy has a long history of finding a way out of apparently intractable political stalemate and newspaper commentators have speculated that in the event of a hung parliament, Berlusconi would seek a broad coalition with the centre-left.

However, the billionaire businessman, who cannot be prime minister in a future government because of a 2013 tax fraud conviction, emphatically ruled this out on Thursday.

"We have all, each one of us, made an absolute pledge to reject coalitions ... with other parties, even if we don't achieve a majority on our own," said the 81-year-old Berlusconi, sitting between Matteo Salvini, head of the far-right League, and Giorgia Meloni, head of the nationalist Brothers of Italy.

Salvini has pushed an anti-immigrant, anti-European message at his rallies, presenting a much more extremist image than the urbane Berlusconi, who has portrayed himself as a moderate.

Critics say the alliance would be unable to hold together in government given their different policy positions.

The Democratic Party, led by former prime minister Matteo Renzi, is expected to come third on Sunday, with the centre-right leading the field and the anti-establishment 5-Star Movement coming second.