CATHOLIC cardinals have held a final day of talks before going into lockdown in the Sistine Chapel to elect a new pope after Benedict XVI's shock resignation, with an Italian and a Brazilian among the top contenders.
The cardinals have been debating the challenges that the next pope will face and vetting possible candidates for the post, as well as airing rare criticism of the Vatican's opaque bureaucracy.
Vatican insiders put Milan Archbishop Angelo Scola in the lead, but short of the two-thirds of the 115 "cardinal electors" needed to become the new leader of the world's 1.2 billion Catholics.
Brazilian Odilo Scherer, the charismatic archbishop of Sao Paolo and Latin America's best hope, is also seen as in with a chance after the red-frocked cardinals begin the storied process, cloaked in secrecy, of choosing one of their peers to lead the church.
The electors must take a solemn oath of secrecy or face excommunication - though no examples of such a fate appear in the record.
"In order of protocol, they will approach the lectern and pronounce the formula of the oath one by one, placing a hand on the Bible," Vatican spokesman Federico Lombardi said.
Some 90 staffers, including cooks, drivers and security guards who will work around the conclave, took the same oath on Monday.
Lombardi said some 5600 media professionals have been accredited to cover the event, which kicks off with a grand mass co-celebrated by the cardinals in St Peter's Basilica on Tuesday at 0900 GMT (2000 AEDT) to invoke divine assistance in their deliberations.
Lombardi said the first round of voting on Tuesday was unlikely to produce a new pope, and told journalists to expect black smoke to emerge from the chimney near the Sistine Chapel about 8pm (0600 AEDT).
In a tradition going back centuries, the cardinals inform the world of a successful election by sending up white smoke, followed soon after by the famous phrase, Habemus Papam (We have a pope).
