Cardinals Set to Elect New Pope
Cardinals have attended a special Mass in Rome, as they prepare to begin voting to elect a new Pope.
The 115 cardinal-electors listened to choirs in St Peter's Basilica as they sought divine guidance for the vote.
They will proceed into the Sistine Chapel later on Tuesday to begin their secret deliberations. They will vote four times daily until two-thirds can agree on a candidate.
The election was prompted by the surprise abdication of Benedict XVI.
There is no clear frontrunner to take over as head of the Roman Catholic Church.
The 85-year-old Benedict stepped down last month saying he was no longer strong enough to lead the Church, which is beset by problems ranging from a worldwide scandal over child sex abuse to allegations of corruption at the Vatican bank.
His resignation and the recent damage to the Church's reputation make the choice of the cardinal-electors especially hard to predict, the BBC's James Robbins in Rome says.
They will weigh pressure for a powerful manager to reform the Vatican against calls for a new Pope able to inspire the faithful, our correspondent adds.
At Tuesday morning's "Mass for the Election of the Supreme Pontiff" in St Peter's Basilica, the cardinals filed in wearing bright red vestments to the sound of Gregorian chanting.
In his homily, the Dean of the College of Cardinals, Cardinal Angelo Sodano, praised the "brilliant pontificate" of Pope Benedict and implored God to grant another "Good Shepherd" to lead the church.
He outlined the mission Catholics believe was given by Jesus Christ to St Peter - the first Pope - emphasising love and sacrifice, evangelisation and the unity of the church.
The BBC's Michael Hirst in Rome says the speech was more measured in tone than the address given in 2005 by Cardinal Joseph Ratzinger before he became Pope Benedict, which featured a fiery attack on the "dictatorship of relativism".
A few hundred people watched the Mass from St Peter's Square on giant screens in thunderstorms and pouring rain.
At 16:30 local time (15:30 GMT), 115 cardinal-electors - all under 80, as those over 80 are excluded - will proceed into the Sistine Chapel for the secret conclave to select Benedict's successor.
Once they have taken an oath of secrecy, Msgr Guido Marini, papal master of ceremonies, will call out the words "Extra omnes" - "Everybody out" - and the chapel doors will be locked to outsiders.
On Tuesday morning several cardinals took to Twitter to say goodbye to their followers before being cut off from the outside world.
"Last tweet before the conclave: May Our Father hear and answer with love and mercy all prayers and sacrifices offered for a fruitful outcome," South African Cardinal Wilfrid Napier tweeted.
Jamming devices in the Sistine Chapel should block all electronic communication and anyone tweeting would in any case risk being excommunicated.
Benedict - now known as Pope emeritus - resigned on 28 February after eight years in office, citing ill health. He was the first Pope in six centuries to do so.
As Cardinal Joseph Ratzinger in 2005, he was the marked favourite ahead of the conclave and was elected pope after just four rounds of voting.
The vote for his successor is expected to take much longer.