Leo XIV's inauguration mass began in St Peter's Square on Sunday, attended by hundreds of dignitaries including US Vice President JD Vance and tens of thousands of faithful.
Chicago-born Robert Francis Prevost, who became the first US head of the world's 1.4 billion Catholics on 8 May, did his first tour of the square in his popemobile ahead of the mass.
Pope Leo XIV made his debut tour of St Peter's Square, greeting tens of thousands of pilgrims and well-wishers ahead of his inauguration mass.
He stood in the white vehicle as it drove through cheering crowds, smiling, waving and making the sign of the cross.
He laid out his priorities for his papacy Sunday, criticising an economic system that exploits nature and the poor during a homily delivered in front of world dignitaries.
"In this our time, we still see too much discord, too many wounds caused by hatred, violence, prejudice, the fear of difference, and an economic paradigm that exploits the Earth's resources and marginalises the poorest," Leo said.
US Vice President JD Vance is among the hundreds of dignitaries due to attend the inauguration mass that begins at 10am local time (0800 GMT).
Leo will preside over the ceremony rich in rites and symbols, where he will receive his special papal ring before giving a homily that will set the tone for his papacy.
After spending two decades as a missionary in Peru, the 69-year-old is unknown to many Catholics, but during the past week he has offered glimpses of the kind of leader he will be.
In meetings with journalists, clergy and diplomats, he repeatedly called for peace in a world full of conflicts and defended social justice.
He also emphasised traditional Catholic values, including the importance of a family built around a "stable union of a man and a woman", and defended the rights of the unborn.
Inacia Lisboa, 71, originally from Cape Verde but who lives in Rome, said she got up early to get a good spot to see a man she said had already "entered my heart".
Asked what she wanted to hear from him, she told AFP: "The first thing is that he prays for us all, for peace in the world -- we need it so much."
Zelensky, Merz
Leo's elevation has sparked huge enthusiasm in the United States, which is being represented on Sunday by Vance, who converted to Catholicism in 2019, and Secretary of State Marco Rubio, also a Catholic.
Before becoming pope, the new pontiff on his personal X account reposted criticism of President Donald Trump's administration over its approach to migration and also pilloried Vance, but the account is no longer accessible.
Vance was the last world leader to meet with Pope Francis, the day before the Argentine died on 21 April, after 12 years as pontiff.
Other notable guests expected include Ukraine's Volodymyr Zelensky -- who memorably met Trump in St Peter's Basilica at Francis's funeral -- and German Chancellor Friedrich Merz.
Peruvian President Dina Boluarte is also on the list provided by the Vatican, along with European Commission President Ursula von der Leyen, Canadian Prime Minister Mark Carney, Israeli President Isaac Herzog, Colombia's Gustavo Petro and a host of European royals.
Italian authorities have deployed thousands of security officers for the event, alongside snipers on rooftops and anti-drone operations.
Fisherman's ring
Leo XIV was elected the 267th pope on 8 May after a secret conclave vote of cardinals that lasted less than 24 hours.
Succeeding the charismatic but impulsive Francis, he takes over a Church still battling the fallout of the clerical child abuse scandal, and trying to adapt to the modern world.
Modernity is not the concern on Sunday, however.
Although no pope has been crowned during an inauguration mass since Paul VI in 1963, the event is still a grand affair steeped in tradition.
Leo will begin by visiting the tomb of Saint Peter -- who in the Christian tradition was one of the Twelve Apostles of Jesus Christ, and the first pope -- located under the altar of the basilica that bears his name.
Leo will then receive the pontifical emblems -- the pallium, a strip of cloth worn over the chasuble, his robe and the fisherman's ring, which is forged anew for each pope and which he will wear on his finger until he dies, when it will be destroyed.
With other cardinals and clergy, the pope will walk in procession into St Peter's Square, where large screens will display the proceedings to the crowds.
At the end of the ceremony, the pope will greet the delegations of heads of state, though it is not clear if any of them will also be accorded a one-to-one private audience.
(AFP)
