Pope Francis I inauguration Mass is being held in St Peter’s Square in Rome, marking the official start of his papacy.
Pope Francis first toured the square in an open-topped vehicle, descending to bless pilgrims behind the barriers.
Up to a million people, along with global political and religious leaders, are attending the Mass.
Pope Francis was elected by a conclave of cardinals last week to take over from Benedict XVI.
Pope Benedict XVI became the first pontiff in 600 years to abdicate last month. Citing his age, 85, he said he could no longer continue in the post.
The first pontiff from the Americas, Francis has suggested he will take a more modest approach than predecessors.
Pope Francis, formerly Argentine Cardinal Jorge Mario Bergoglio, left his temporary residence at Casa Santa Marta shortly before 09:00 and began touring St Peter’s Square.
The pontiff waved to the hundreds of thousands of pilgrims, who flew flags and shouted: “Long live the Pope!”
Pope Francis I inauguration Mass is being held in St Peter’s Square in Rome, marking the official start of his papacy
Pope Francis then entered St Peter’s Basilica and donned his vestments.One of the Pope’s first duties was to go down to the tomb of St Peter to venerate it.
Pope Francis was then presented with his papal pallium made of lambs’ wool – symbolizing his role as shepherd of his flock – in the main square.
He also received the “fisherman’s ring” bearing the image of St Peter holding two keys. The ring is second hand and is made of silver-plated gold, not the solid gold worn by Francis’ predecessor.
With the reception of the pallium and ring, Francis officially began his office as the 266th pope.
The Pope then received the obedience of the cardinals, and the Mass formally began.
Pope Francis then delivered his homily, in Italian.
It began by focusing on Joseph and his role as protector – of Mary, Jesus and the Church.
Pope Francis I, born Jorge Mario Bergoglio on 17 December 1936, is the 266th and current Pope of the Catholic Church, elected on 13 March 2013.
He is the first Pope born in the Americas, and the first Pope from the Southern Hemisphere.
Cardinal Jorge Mario Bergoglio, Archbishop of Buenos Aires has been mooted as a possible successor ever since John Paul II died.
Jorge Mario Bergoglio, 76, a trained chemist and son of a railway worker, has been a cardinal since 2001 and is widely seen as being open and compassionate.
He stands out for his humility, living in a modest apartment, rather than his luxury official residence.
“In favor of Bergoglio is his pastoral attitude, as they say in the Church – his relationship with the people,” said in 2005 Leandro Pastor, a philosophy professor at the University of Buenos Aires, who has known Cardinal Bergoglio for more than 30 years.
“He’s a very simple man. He’s very austere. And also, I think he’s an intelligent man and someone who is very good at communicating.”
Pope Francis I, born Jorge Mario Bergoglio, is the 266th and current Pope of the Catholic Church
Jorge Mario Bergoglio impressed fellow prelates in 2001 when he skilfully helped to manage a synod of bishops in Rome.
Buenos Aires’ cardinal is also a strong advocate for the poor. And, as a Latin American, he comes from a region which is home to around half the world’s billion or so Catholics.
He speaks Italian – the official language of the Church – and that he traces his ancestry back to Italy.
In the event that cardinals struggle to decide whether to maintain a non-Italian papacy or to return to its traditional roots, Jorge Mario Bergoglio could emerge as a choice of compromise.
For the past 28 years, Jorge Mario Bergoglio has lived with only one functioning lung, although he is said to be in good shape.
And then there is the fact that he is a Jesuit.
This order of the Church has never produced a Pope before.
Jorge Mario Bergoglio, the archbishop of Buenos Aires, has been elected the 266th Roman Catholic Church’s new Pope.
The Argentine cardinal is the first Latin American to be Pope.
He will call himself Francis I.
An hour earlier, white smoke billowing from the Sistine Chapel chimney announced to the world that cardinals gathered inside had made their choice.
Jorge Mario Bergoglio replaces Benedict XVI, who resigned last month saying he was not strong enough to lead the Church.
The 115 cardinals have been in isolation since Tuesday afternoon, and held four inconclusive votes.
Jorge Mario Bergoglio, the archbishop of Buenos Aires, has been elected the 266th Roman Catholic Church’s new Pope
At least 77 of them, or two-thirds, would have had to vote for a single candidate for him to be elected Pope.
Before the conclave began, there was no clear frontrunner to replace Benedict.
Crowds with umbrellas massed in the square flying flags from around the world.
The Catholic News Agency said people were running through the streets of Rome, hoping to reach St Peter’s Square in time for the appearance of the new Pope.