A crowd waving League and Italian flags filled Piazza San Giovanni, traditionally a venue for leftist and trade union rallies, as League leader Matteo Salvini and his allies spoke from a stage against a huge backdrop reading "Italian Pride".

"This is the Italy that works and suffers, that dreams and hopes," said Salvini, who was deputy prime minister and interior minister in the previous coalition of the League and the anti-establishment 5-Star Movement.

That government collapsed in August when Salvini, encouraged by surging poll ratings, pulled out in a failed bid to trigger elections he hoped would crown him as prime minister.

Instead, 5-Star formed a new coalition with the centre-left Democratic Party (PD), pushing the League into opposition.

"We are the people against the elite, we will change the history of this country," said Salvini, adding that 200,000 people had turned out at Saturday's rally.

The police estimated a figure closer to 50,000.

Opinion polls show the League has lost some support since Salvini brought down the previous government, but it remains easily Italy's most popular party, with around 30 per cent of the vote.

However, the combined backing of the PD, 5-Star and other allied leftist and centrist groups is roughly the same as the support for the rightist parties gathered at Saturday's rally.

Salvini was preceded on the stage by 83-year-old former prime minister Silvio Berlusconi, whose conservative Forza Italia party has steadily lost support in recent years, and Giorgia Meloni, who heads the far-right Brothers of Italy party.

Australian Associated Press