Pope Francis has already appeared in St Peter's Square in Rome ahead of the inauguration mass that marks the official start of his papacy.

BBC reports Francis has  toured the square in a papal vehicle, descending to bless pilgrims behind the barriers.

Up to a million people, along with global political and religious leaders, are attending the mass.

Papal ringPope Francis left his temporary residence at Casa Santa Marta shortly before 10:00 am Bulgarian time to begin touring St Peter's Square.

Francis has now entered St Peter's Basilica to don his vestments.

The mass began at 10:30 am when the Pope goes down to the tomb of St Peter to venerate it.

According to BBC, Francis will then be presented with his papal pallium made of lambs' wool and the "fisherman's ring" bearing the image of St Peter holding two keys.

The ring is second hand and is made of silver-plated gold, not the solid gold worn by Francis' predecessor.

The Mass then formally begins in the main square, co-celebrated by around 180 clergymen, including Adolfo Nicolas, the superior general of Pope Francis' Jesuit order.

Top-level delegations from 180 countries are attending the enthronement. The ceremony is be joined by Royals from Britain, Spain and Belgium.

Bulgarian President, Rosen Plevneliev and leaders from around the world will greet the Head of the Roman Catholic Church.

The US is represented by Vice President Joe Biden, Argentina - by President Cristina Fernandez de Kirchner, Brazil - by President with Bulgarian roots Dilma Rousseff.

Ecumenical Patriarch Bartholomew is also going present at the ceremony, which is to be attended by one million people. His visit is seen as a gesture aiming to improve relations between the Christian Orthodox and Catholic Churches.

He will be the first Orthodox patriarch to attend a papal inauguration mass since the two branches of Christianity split more than 1 000 years ago.

Thirty-three groups of guests from various Christian Churches are expected in total, according to the Vatican, along with 16 delegations from Jewish communities, as well as representatives of other faiths.

Communion will be distributed by 500 priests throughout the crowd.

Several Bulgarian TV channels are airing the ceremony live.

The election of Cardinal Jorge Mario Bergoglio surprised many observers when it was revealed on Wednesday.

Although, during the 2005 conclave, he reportedly came second to Pope Benedict XVI, who withdrew from the post earlier, few had predicted the election of the first pope from outside Europe in 1 300 years.

Francis, 76, is the first Latin American - and the first Jesuit - Pope. He already gave firm signs he is to stamp his style on the papacy in applauding media and informing the Catholic Church would become "a compassionate NGO" without spiritual renewal.