Vatican City: Cardinals moved into the Vatican on Tuesday as the suspense mounted ahead of a secret papal election with no clear frontrunner to steer the Catholic world through troubled waters after Benedict XVI's historic resignation.
The 115 cardinal electors who pick the next leader of 1.2 billion Catholics in a conclave in the Sistine Chapel will live inside the Vatican walls completely cut off from the outside world until they have made their choice.
In a series of centuries-old rituals on Tuesday, cardinals will be sworn in with a solemn oath that threatens anyone who reveals the deliberations of the conclave with instant excommunication.
Dozens of Vatican staff working on the conclave, including cooks, drivers and security guards, swore the oath on Monday and jamming devices have been installed to prevent any bugging or communication in or out of the chapel.
The prayers will begin with a special mass called "For the Election of the Roman Pontiff" in St Peter's Basilica starting at 0900 GMT.
Cardinals will later file into the Sistine Chapel from 1530 GMT chanting in procession to invoke the Holy Spirit to inspire their choice.
The cardinals are set to hold a first round of voting later on Tuesday -- but the Vatican has already said it expects the smoke from the burning of the ballots to be black indicating no papal election has taken place.
Ballots on subsequent days will be burnt at around 1100 GMT after two rounds of voting in the morning and at around 1800 GMT after two rounds in the afternoon -- the smoke is famously turned white if there is a new pope.
Catholics around the globe have been praying for the conclave, which is expected to last no more than a few days.
"We'll be praying for the cardinals until a decision is made, it's the part we play in the conclave," said sister Celestina, 62, a nun from Croatia, kneeling in a church near the Vatican.
"The Church is like a boat, all the faithful are sailing in it together but we're without a helmsman at the moment."
Among the possible candidates, three have emerged as favourites -- Italy's Angelo Scola, Brazil's Odilo Scherer and Canada's Marc Ouellet, all of them conservatives cast in the same mould as "pope emeritus" Benedict XVI.
But the rumour mill in the Vatican has thrown up more names too including cardinals from Austria, Hungary, Mexico, the Philippines, South Africa and the United States -- many of them inspiring pastoral figures in their communities.
The field is wide open although a few key aims unite many of the cardinals after Benedict's rocky eight-year papacy -- reform the intrigue-filled Vatican bureaucracy, counter rising secularism in the West and find new inspiration for Catholics in the way John Paul II did.
The scandal over decades of sexual abuse of children by paedophile priests -- and the efforts made by senior prelates to cover up the crimes -- has cast a long shadow over the Church that will be an ongoing challenge for any new pope.
There have been calls from within the Church too for a rethink of some basic tenets such as priestly celibacy, the uniform ban on artificial contraception and even allowing women to be priests as in other Christian denominations.
"We need someone able to provide the Church with what it needs in today's world, someone who will help it open up to the world and listen to the people," said Roger Seogo, a priest from Burkina Faso in west Africa visiting the Vatican.
The tradition of holding conclaves goes back to the 13th century when cardinals were locked into the papal palace in Viterbo near Rome by a crowd of angry townspeople because they were taking too long to make their decision.
That conclave still dragged on for nearly three years but the rules have been reworked since then and the longest conclave in the past century -- in 1922 -- lasted only five days. Benedict's election took just two days.
Benedict stunned the world on February 11, announcing that he no longer had the strength of body and mind to keep up with a fast-changing modern world shaken by vital questions for the Roman Catholic Church.
In a series of emotional farewells attended by tens of thousands of supporters, 85-year-old Benedict said he would live "hidden from the world" and wanted only to be "a simple pilgrim" on life's last journey.
Vatican experts have said the German's decision, which makes him only the second pope to resign by choice in the Church's 2,000-year history, could mean future popes will also step down once their strengths begin to fail them.
Cardinals prayed for divine guidance at their last Sunday masses before the conclave in churches across Rome.
Ouellet said this was a "unique time in history for the Church", adding: "The whole world is waiting".
"We pray that the Holy Spirit may indicate to the cardinals the one that God has already chosen," he said.
US Cardinal Sean O'Malley -- also a possible contender -- said in his homily: "Let us pray that the Holy Spirit enables the Church to choose a new pope who will confirm us in our faith and make more visible the love of the Good Shepherd."