An Italian judge reviewing charges against far-right leader Matteo Salvini that he illegally detained migrants at sea delayed the hearing until November 20 so he could hear from senior members of the government, including Prime Minister Giuseppe Conte.

Salvini made no comment as he went into the closed door hearing at the Catania court house which was held to determine whether he should face trial on charges that he abused his powers as then-interior minister to block 116 migrants from disembarking from the Italian Gregoretti coastguard boat last year, under his so-called "closed ports" policy.

He faces a maximum sentence of 15 years.

If the opposition leader and head of the anti-immigrant League party is convicted for more than two years, he could well also be barred from holding public office for six years, preventing him from running for prime minister at the next election in 2023.

Salvini's defence counsel as well as the prosecutor called for the case to be dismissed.

But Judge Nunzio Sarpietro decided instead to hear from current Interior Minister Luciana Lamorgese and Foreign Minister Luigi Di Maio, along with Prime Minister Conte, before making such a decision.

Salvini, who had some sharp words on the hearing earlier in the week, appeared satisfied with the outcome.

"It is not a political process. I found the judge to be a free person," he said, after having previously berated the local authorities for pursuing him while not doing anything about the mafia and serious crime.

"The Italian justice system is a system which works," he said Saturday.

Salvini arrived in Catania on Thursday for three days of rallies, dinners and debates on issues from immigration to security in the city's port area.

The League printed t-shirts and advertised cheap flights for the "Italians choose freedom" festival, which will feature fellow far-right head Giorgia Meloni, of the Brothers of Italy party, and bigwigs from ex-premier Silvio Berlusconi's Forza Italia.

Fellow rightwing travellers in Italy backed Salvini, with Giovanni Toti, regional president of Liguria and a Forza Italia member, slamming what he termed "the most absurd trial in the history of the Italian Republic."

A 500-strong police force was tasked with preventing clashes between Salvini fans and leftwing protesters.

Matteo Salvini is due to address a rally after his hearing on Saturday
Matteo Salvini is due to address a rally after his hearing on Saturday AFP / Andreas SOLARO

Salvini had vowed to "plead guilty of having defended Italy and Italians".

Among his accusers are a Nigerian family who claim they were "treated worse than animals" and are a civil party in the case.

The 116 migrants, mainly from Sudan, as well as central and western Africa, were rescued in the Mediterranean in two separate operations on July 25 last year after five days at sea.

They were transferred to the Gregoretti on July 26, then held on the overcrowded patrol vessel under the fierce summer sun despite a scabies outbreak and a suspected case of tuberculosis.

Fifteen unaccompanied minors were eventually allowed off on July 29 following pressure from Catania's juvenile court.

The remaining migrants disembarked on July 31 after Salvini, 47, said a deal had been brokered with EU countries to take them.

His defence team insists the decision to hold them was not Salvini's alone, but reached collectively within the government.

Salvini, who has said Sicilian judges would be better off concentrating on jailing mafiosi than trying him, declared that it would be "the Italians, in the next elections, who will say whether I did the right thing or not".

Senators lifted his parliamentary immunity last February.

Analysts say the legal trouble is unlikely to hurt Salvini's popularity, but could in fact work in his favour.

Salvini's fierce "Italians First" stance saw his popularity shoot up as interior minister, though his polling numbers slid significantly during the coronavirus lockdown, which overshadowed the migrant question.

With the centre-left government promising to water down Salvini's harsh security decree which makes it easier to expel migrants, the stage is set for a fresh political showdown.

The far right is hoping to cash in once more on a vote-winning issue.