The former archbishop of Buenos Aires, Cardinal Jorge Bergoglio, entered the St Mary Major basilica through a side entrance just after 8 am (0700 GMT) and left about 30 minutes later. He had told a crowd of some 100,000 people packed in rain-soaked St Peter's Square just after his election that he intended to pray tomorrow to the Madonna "that she may watch over all of Rome".
He told cardinals he would also call on retired Pope Benedict XVI on Friday and celebrate an inaugural Mass in the Sistine Chapel, where cardinals on Wednesday elected him leader of the 1.2 million-strong church in an unusually quick conclave.
Francis, the first Jesuit pope and first non-European since the Middle Ages, decided to call himself Francis after St Francis of Assisi, the humble friar who dedicated his life to helping the poor.
The new pope immediately charmed the crowd in St Peter's that roared when his name was announced.
Waving shyly, he said the cardinals' job was to find a bishop of Rome. "It seems as if my brother cardinals went to find him from the end of the earth, but here we are. Thank you for the welcome."
The 76-year-old Bergoglio, said to have finished second when Pope Benedict XVI was elected in 2005, was chosen on just the fifth ballot to replace the first pontiff to resign in 600 years. In the past century, only Benedict, John Paul I in 1978 and Pius XII in 1939 were elected faster.
Francis spoke by phone with Benedict, who has been living at the papal retreat in Castel Gandolfo, and was to visit him on Friday, according to US Cardinal Timothy Dolan.
The visit is significant because Benedict's resignation has raised concerns about potential power conflicts emerging from the peculiar situation of having a reigning pope and a retired one.
Vatican City: Pope Francis opened his first morning as pontiff by praying on Thursday at Rome's main basilica dedicated to the Virgin Mary, a day after cardinals elected him the first pope from the Americas in a bid to revive a Catholic Church in crisis and give it a preacher with a humble touch.
First Published: Thursday, March 14, 2013, 16:25