Francis was visiting Sicily to honour a priest killed by mob henchmen in 1993 for trying to protect youths from the clutches of organised crime.

The day-long trip by Francis to the Mediterranean island where the Italian Mafia is rooted marked the 25th anniversary of the assassination of the Reverend Giuseppe "Pino" Puglisi.

Puglisi was declared a martyr by the Vatican and was beatified in 2013, the last formal step before possible sainthood.

Francis paid tribute to the priest, who worked to keep unemployed youths in a poor neighbourhood of Palermo from turning to local Mafia bosses for jobs like pushing drugs.

The papal pilgrimage came amid revelations about priests and bishops who sexually abused children or connived to protect the abusers in various nations.

Tens of thousands of people cheered Francis at an open air mass held in the late morning at an esplanade along the port city's waterfront.

A large banner carried by young people in the crowd as Francis was driven by in his white popemobile read "Let's renew the church".

Pressure is building on Francis to say what he knew about the sexual misconduct of US prelate Theodore McCarrick, who was recently stripped of his cardinal's rank by the pope.

Francis drew applause as he told the crowd, "If the Mafia threat is 'you will pay me,' the Christian prayer is 'Lord, help me to love.'

"Thus I say to the Mafiosi: change, brothers and sisters. Quit thinking about yourselves and your money," Francis continued in his homily.

"You know, a funeral shroud doesn't have pockets. You can't take it with you," he said of organised crime's ill-gained wealth from drug and arms trafficking, extortion and betting and prostitution rackets.

Australian Associated Press