As the Mass began, Francis was presented with his papal pallium and the fisherman's ring bearing the image of St Peter. With this, Francis officially became the 266th pope.

Pope Francis' homily at the Mass on Tuesday began by focusing on Joseph and his role as protector - of Mary, Jesus and the Church.

The Pope also stressed the importance of the environment: "It means protecting all creation, the beauty of the created world... It means respecting each of God's creatures and respecting the environment in which we live," he said.

Pope Francis called on "all those who have positions of responsibility in economic, political and social life to be protectors of creation." He said, "let us not allow omens of destruction and death to accompany the advance of this world."

In celebrating the Mass, Pope Francis was joined by 180 clergymen, including Adolfo Nicolas, the superior general of the Jesuit order. Pope Francis is the first Jesuit priest to become pope. The Pope later greeted assembled dignitaries individually in St Peter's Basilica.

Speaking to 200,000 people gathered in the sunshine in St. Peter's Square, Pope Francis repeated his central message that the Church's mission was to defend the poor and disadvantaged.

In a simpler style than his predecessor, the new Pope has indicated that his strategy for repairing the reputation of the Catholic Church is by reviving basic Christian teaching.

The name he chose for himself, Francis, remembers St Francis of Assisi, the 13th-Century son of an aristocrat who ended a life of luxury to live in poverty.

Pope Francis had begun the day by touring St Peter's Square in an open-topped car but left it on foot to bless a disabled man by the barriers.

Celebrating in Argentina

Born in Buenos Aires, Argentina as Jorge Mario Bergoglio, the son of an Italian immigrant railway worker, Pope Francis also remembered the faithful gathered in his home city where he was Archbishop.

Hundreds of people had 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.

In a special message Pope Francis said: "My dear children, I know you're in the plaza. I know that you're making prayers. I need them very much."

Social Media and Diplomacy

Francis also took to Twitter using the account set up by his predecessor in an attempt to bring the Catholic message to young people: "Let us care for one another," he tweeted as @Pontifex.

German Chancellor Angela Merkel, the daughter of a Protestant pastor, found the mass "emotional," according to a German government spokesman. She was said to be "impressed by the simple and direct way of speaking" of the new pope.

jm/mz (Reuters, AFP)