Matteo Salvini, Italian ex-Interior Minister has gone on trial in Sicily, accused of preventing a migrant boat from docking in August 2019.
The right-wing politician denies kidnap and dereliction of duty charges.
Prosecution witnesses include Hollywood actor Richard Gere, who was on board.
Mr Salvini closed ports to rescue boats, leaving dozens of migrants saved from the Mediterranean stranded aboard a Spanish rescue vessel for three weeks in deteriorating conditions.
He faces a maximum of 15 years in jail if convicted.
On the opening day of the trial, the judge allowed all witnesses submitted by both sides to testify. They also include former Prime Minister Giuseppe Conte and members of his cabinet.
But the defendant mocked Mr Gere’s presence.
“I wonder if it’s serious that Richard Gere of Hollywood is going to testify about my behaviour at a trial,” he told journalists outside the court.
Mr Gere had boarded the Spanish ship the Open Arms before it docked after 19 days at sea on the island of Lampedusa with nearly 150 migrants on board.
Mr Salvini said he was defending his government’s “closed ports” policy aimed at stopping migrants from making the dangerous Mediterranean crossing.
But his blockade of the ship caused an outcry and a serious split in the coalition government at the time. His League party was in a coalition with the anti-establishment Five Star, but now he is an opposition MP.
In July last year, the Senate voted to strip him of his parliamentary immunity.
Mr Conte had called Mr Salvini “obsessed” with keeping migrants out of Italian ports.
In 2019 the Open Arms charity filed a legal complaint against Mr Salvini’s block on their ship, which ended on 20 August.
By that time, many of the migrants had already been allowed off the ship.
The charity’s founder Oscar Camps told reporters outside the trial on Saturday that saving lives should not be politicised.
“Rescuing people in the sea is no crime, it’s an obligation not only for the captain but also for all states,” he said.
The court adjourned after several hours. A further hearing has been scheduled for December 17.