Pope Francis has issued a strong appeal for the protection of the environment and the defence of the weakest members of society during his his inaugural mass.
Up to 200,000 people, including world political and religious leaders, attended the Mass in St Peter's Square in Rome on Tuesday to witness the pope's formal installation as the new leader of the Catholic Church.
Before the mass got under way, Pope Francis, wearing his papal whites and standing in the middle of an open-topped vehicle, waved, smiled and gave the thumbs up to the ecstatic crowds.
Pope Francis's homily at the mass focused on defending the poor and the weak and he urged the world to shun "the omens of destruction and death".
"It means respecting each of God's creatures and respecting the environment in which we live," he said.
"It means protecting people, showing loving concern for each and every person, especially children, the elderly, those in need, who are often the last we think about."
Francis had begun the day by touring St Peter's Square in the Popemobile.
Hundreds of thousands of people were there to see him and at one point he stepped down from the vehicle and approached the barriers to bless a disabled man.
He then entered St Peter's Basilica and donned his vestments.
Francis was elected by a conclave of cardinals last week to take over from Benedict XVI.
Benedict 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.
Hundreds of people also gathered in the early hours of Tuesday in Plaza de Mayor, the main square in Buenos Aires, to watch the Mass broadcast on giant screens set up outside the cathedral.
Meanwhile Argentine president Cristina Fernandez de Kirchner says she has asked Pope Francis to intervene with Britain in the long-running dispute over the Falkland Islands.
Ms Fernandez had lunch with the Pope, a former Archbishop of Buenos Aires, in the Vatican during a visit to Rome to attend his installation mass.
"I asked for his intervention to avoid problems that could emerge from the militarisation of Great Britain in the South Atlantic".