Pope Francis I celebrated his inauguration mass in front of one million worshippers who had gathered in St Peter's Square and called for the Church to serve its flock and not be afraid of kindness.
Francis's first homily as pontiff was in line with the humble style he has shown since his election by the cardinals' conclave. The Pope used St Francis of Assisi, whose name he took, as an example for the whole Catholic Church, starting from the top down.
"We ought to respect every living creature and especially the weakest, as St Francis taught us," the Pope said. "We shouldn't be afraid of kindness and tenderness."
Before entering St Peter's Basilica, the Argentinian pontiff, 76, toured the square aboard a white "Popemobile". He got out of the vehicle to bless a disabled man in a wheelchair.
The mass began with a cardinal intoning the rite of inauguration:"The Good Shepherd charged Peter to feed his lambs and his sheep; today you succeed him as the bishop of this church."
Then Francis received the woollen pallium, or stole, symbolising his role as shepherd of his flock, and also a gold-plated silver fisherman's ring that is a symbol of the papacy.
Francis, known prior to the election as Cardinal Jorge Bergoglio of Buenos Aires, was elected 266th pontiff of the Catholic Church to succeed Benedict XVI who announced his resignation in February.
Francis's first words during his homily were dedicated to his predecessor. He said Benedict would be in his prayers.
Bergoglio said that Christ had entrusted him with a great power "to serve humbly and concretely all of God's people and embrace with tender affection the whole of humanity, especially the poorest, the weakest, the least important".
Francis called for global leaders to work for the world's good and not allow "destruction and death to scar out path".
About 130 official delegations and religious leaders from around the world attended the mass.
According to leaks from within the conclave, Bergoglio was elected with an extraordinary majority of votes, far more than the 77 needed.
Bergoglio was also said to have been the runner-up in the 2005 conclave that saw Ratzinger elected.