The cardinals, including the 115 aged under 80 who will vote for the next pope, filed into St Peter's Basilica on Tuesday as choirs sang at the ritual solemn mass that precedes a conclave.
They prayed that God would inspire them to choose the right man to replace Pope Benedict XVI, who abdicated abruptly last month saying he was not strong enough to confront the woes of a church whose 1.2-billion members look to Rome for leadership.
The mass was the last event for the cardinals as a group before they enter the Sistine Chapel on Tuesday afternoon and make their choice for the next pontiff before Michelangelo's famous fresco of the Last Judgment.
In his homily, Italy's Angelo Sodano, dean of the cardinals, said they should pray "that the Lord will grant us a pontiff who will embrace this noble mission with a generous heart".
He called for unity within the church and urged everyone to work with the next pope, whoever he should be.
The secret conclave, steeped in ritual and prayer, could carry on for several days, with no clear favourite in sight.
Vatican insiders say Italy's Angelo Scola and Brazil's Odilo Scherer have emerged as the men to beat. The former would bring the papacy back to Italy for the first time in 35 years, while the latter would be the first non-European pope in 1 300 years.
However, a host of other candidates from numerous nations have also been mentioned, including US cardinals Timothy Dolan and Sean O'Malley, Canada's Marc Ouellet and Argentina's Leonardo Sandri.
Known as the "princes of the church", the cardinals will only emerge from their seclusion once they have chosen the 266th pontiff in the 2 000-year history of the church, which is beset by sex abuse scandals, bureaucratic infighting, financial difficulties and the rise of secularism.
Many Catholics are looking to see positive changes.
"It's not an anxious moment, but a moment of great hope. The first thing the church should do is return to the lives of the people, instead of losing itself in theology," said Italian Andrea Michieli (22), who attended the mass.
"The new pope should give a young image of the church so everyone sees the church is not just the curia," he said referring the Vatican's central bureaucracy which has been criticised for failing to prevent a string of mishaps during Benedict's troubled, eight-year reign.
Mexico's cardinal Norberto Rivera Carrera told Italy's La Stampa newspaper there were many different views about the right profile for the next pontiff, with some wanting an academic, others seeking someone close to the people, or else a good manager.
Asked if the conclave could therefore drag on, he said: "I do not think it will be long because there are diverse opinions. We will come to an agreement very quickly."
The average length of the last nine conclaves was just over three days and none went on for more than five days.
Division among cardinals
Signalling the divisions among the cardinals, Italian newspapers reported on Tuesday an open clash between prelates in a pre-conclave meeting on Monday.
The newspapers said the Vatican hierarchy's number two under Benedict, Tarcisio Bertone, had accused Brazil's João Braz de Aviz of leaking critical comments to the media. Aviz reportedly retorted that the leaks were coming from the curia, earning loud applause.
All the red-hatted prelates in the Sistine Chapel were appointed by either the German-born Benedict XVI or his Polish predecessor John Paul II, and the next pontiff will almost certainly pursue their fierce defence of traditional moral teachings.
But Benedict and John Paul were criticised for failing to reform the Vatican bureaucracy, battered by allegations of intrigue and incompetence, and some church people believe the next pope must be a good chief executive or at least put a good management team in place under him.
Vatican insiders say Scola, who has managed two big Italian dioceses, might be best placed to understand the Byzantine politics of the Vatican administration – of which he has not been a part – and therefore be able to introduce swift reform.
The curia faction of cardinals working inside the Vatican bureaucracy is said by the same insiders to back Scherer, who worked in the Vatican's Congregation for Bishops for seven years before later leading Brazil's São Paulo diocese – the largest in the country that has the largest national Catholic community.
Concerning growth of Islam
With only 24% of Catholics living in Europe, pressure is growing within the church to choose a pontiff from elsewhere in the world who would bring a different perspective.
Latin American cardinals might worry more about poverty and the rise of evangelical churches than questions of materialism and sexual abuse that dominate in the West, while the growth of Islam is a major concern for the church in Africa and Asia.
The cardinals are expected to hold their first vote late on Tuesday afternoon – which is almost certain to be inconclusive – before retiring to the Vatican hotel for the night.
They hold four ballots a day from Wednesday until one man has won a two-thirds majority – or 77 votes. Black smoke from a makeshift chimney on the roof of the Sistine Chapel will signify no one has been elected, while white smoke and the pealing of St Peter's bells will announce the arrival of a new pontiff.
As in mediaeval times, the cardinals will be banned from communicating with the outside world. The Vatican has also taken high-tech measures to ensure secrecy in the 21st century, including electronic jamming devices to prevent eavesdropping.
Cardinals earlier began moving into the Vatican's Santa Martha hotel, where they will live during the conclave. – Reuters