VATICAN CITY (AFP) - Pope Francis knelt at the tomb of St Peter and donned a ring symbolising his new papal powers at a sumptuous inauguration on Tuesday as tens of thousands of pilgrims cheered Latin America's first pontiff.

Pope Francis swept into a sun-drenched St Peter's Square to greet the throngs and walked in a procession along the length of the basilica as prelates chanted a Litany of Saints in Latin.

The 265th successor to St Peter, considered the first pope, also received from his cardinals the pallium - a lambswool strip of cloth that symbolises the pope's role as a shepherd.

The "Fisherman's Ring" bestowed on him by Angelo Sodano, the dean of the college of cardinals, is a personalised signet ring traditionally worn by popes in honour of St Peter - a fisherman.

Crowds had gathered from the early morning to see the Argentine pope's enthronement in a rare ceremony laden with centuries-old rituals and lavish imagery.

Pope Francis gave the thumbs-up to ecstatic crowds and stopped to kiss babies, getting off the car at one point to bless a handicapped man.

"With Pope Francis, the Church will be closer to the people and to the modern world," said Rodrigo Grajales, a 31-year-old Colombian priest.

The former archbishop of Buenos Aires, Jorge Mario Bergoglio has already won hearts in Rome with a disarmingly informal style which contrasted with Tuesday's pomp and ceremony.

The Vatican said 132 foreign delegations attended.

Bergoglio was the surprise choice at a conclave of cardinals to find a successor to 85-year-old Benedict XVI, who last month brought a sudden end to a papacy that had often been overshadowed by scandal, saying he was too old to carry on. He was the first pope to resign since the Middle Ages.

The jovial Francis has said he chose his papal name in honour of the mediaeval Italian saint St Francis of Assisi and has called for a "poor Church for the poor", warning the world's cardinals against pursuing worldly glories.

"Go Francis! We Will Be With You Wherever You Go!" read a sign held up by a group of Brazilian nuns in St Peter's Square.

Sister Rosa, an elderly Italian nun, said she expected the pope would be "another St Francis on Earth for love, goodness, poverty and humility".

The son of an Italian immigrant railway worker from a working-class quarter of Buenos Aires has been effusive in a way that is unusual in the Vatican.

But the arrival of world leaders has presented him with a first diplomatic headache in the form of a request from compatriot President Cristina Kirchner of Argentina to mediate in a row with Britain over sovereignty of the Falkland Islands.

Pope Francis is still haunted by criticism at home for failing to speak out against the excesses of Argentina's military rule during the dictatorship of the 1970s and 1980s.

The Chinese government has also said it will not be sending any representatives after Taiwanese President Ma Ying-jeou said he was attending.

Zimbabwean President Robert Mugabe also flew in, sidestepping an EU travel ban over human rights abuses that does not apply to the Vatican.

Latin America was heavily represented at the inauguration of the first non-European pope in nearly 1,300 years, with the presidents of Argentina, Brazil, Chile, Costa Rica, Mexico and Paraguay all in attendance.

German Chancellor Angela Merkel, Spanish Prime Minister Mariano Rajoy, French Prime Minister Jean-Marc Ayrault and European Union leaders were also present.

Leaders of the Eastern Catholic Rite were also in attendance, including Bartholomew I, the Ecumenical Patriarch of Constantinople.

Vatican radio said it was the first time a patriarch of Constantinople had attended an inauguration since 1054 when the eastern and western halfs of Christendom split.

The Vatican was in security lockdown for the event, with 3,000 officers deployed including sharpshooters on the rooftops and bomb disposal experts.

Three Red Cross tents could be seen on the square and giant screens have been placed all down Via della Conciliazione - the main avenue leading to St Peter's.

The mass proper will include a homily by Pope Francis, who has often strayed from prepared texts with off-the-cuff jokes, anecdotes and passionate exhortations for spiritual renewal.

Church leaders have urged Pope Francis to move quickly to reform the intrigue-filled Roman Curia, the central administration of the Roman Catholic Church, and his appointments in the coming weeks will be closely watched.

He has indicated he will press for a friendlier faith that is closer to ordinary people and for social justice, although the moderate conservative is unlikely to change major tenets of Catholic doctrine.

Vatican experts say he has also signalled he will pursue a more inclusive "collegial" style of leadership together with the cardinals and bishops.

Vast crowds also gathered on the other side of the Atlantic outside the Buenos Aires cathedral to dance and sing as they watched the inauguration.

Catholic high school students chanted slogans praising Francis, while seminarians and nuns waved Vatican flags and signs supporting the new pope.

"This pope has awakened deep emotions within me, not only because he's from Argentina, but because of his warmth as a person," Ms Celia Farias, 33, told AFP. "As a Catholic, it has renewed my faith."