POPE Francis has opened his pontificate with a visit to Rome's main basilica dedicated to the Virgin Mary.

The visit came the day after cardinals elected him the first pontiff from the Americas in a bid to resurrect a Catholic Church in crisis.

The former archbishop of Buenos Aires, Jorge Bergoglio, entered the basilica through a side entrance and left about 30 minutes later, Italy's RAI state television said.

He told a crowd of 100,000 people packed into a rain-soaked St Peter's Square just after his election on Wednesday that he intended to pray to the Madonna "that she may watch over all of Rome". He told cardinals he would also call on retired Pope Benedict XVI and celebrate an inaugural mass in the Sistine Chapel.

Francis visited St Mary Major basilica the day after cardinals elected him leader of the 1.2 million-strong church in an unusually quick conclave.

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 charmed the crowd in St Peter's which 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, said to have finished second when Pope Benedict XVI was elected in 2005, was chosen on 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 is to visit him on Friday, according to US Cardinal Timothy Dolan.