Pope Francis on Sunday completed his installation as pontiff at an emotional ceremony in which he formally took possession of Rome's St John Lateran basilica -- the official seat of the city's bishop.
The pope was driven around the square in front of the basilica in an open-topped car with a crowd of thousands chanting "Long live the pope!" and one group holding up a banner reading: "We Love You!"
The leader of the world's 1.2 billion Catholics smiled and kissed children held up to him by members of his security detail, taking off his white skullcap because of the strong wind.
Latin America's first pontiff spoke to and embraced one-by-one a long line of elderly and disabled people in wheelchairs in emotional scenes that drew rounds of applause from the congregation.
"God always waits for us, even when we have left him behind," Francis, the first non-European pope in nearly 1,300 years, said in his homily.
"We hear many offers from the world around us but let us take up God's offer instead," he said.
"God's patience has to call forth in us the courage to return to him, however many mistakes and sins there may be in our life," he added.
After the mass, Francis addressed the crowd in the square saying: "Thank you for being here. I ask you to pray for me. I need it. Don't forget!
"Let's go forward together -- people and bishop together," said the pope, who has stressed the importance of his role as bishop of Rome.
With a series of significant symbolic gestures, the 76-year-old has shown that he intends to bring the Church closer to ordinary people, to reach out to the needy and to shake up Vatican traditions.
Experts are watching closely for the pope's appointments to key Vatican posts in the coming days, however, for signs of concrete action on challenges including the need for root-and-branch reform of the scandal-hit Vatican bureaucracy.
The pope, who named himself after St Francis of Assisi saying he was inspired by the saint's actions to alleviate poverty and promote peace, appointed the Spanish leader of the main Franciscan order to a top post on Saturday.
The pope, formerly the archbishop of Buenos Aires Jorge Bergoglio, was elected in a conclave on March 13 and his inauguration was on March 19.
His predecessor Benedict XVI brought to an abrupt end a troubled pontificate in February, saying he was too weak in mind and body to carry on.
Earlier on Sunday, Francis spoke to 100,000 pilgrims in St Peter's Square at one of his traditional weekly blessings, urging them to evangelise and "not be afraid to be Christians".
"We must have the courage to go out and proclaim the risen Christ," he said.