The historic conclave to choose a successor for the first pope to resign in over 700 years begins on Tuesday, with the world in suspense over a secret election with no clear frontrunner.

Italian carabinieri police stand in front of St Peter's square on March 11, 2013 at the Vatican. The historic conclave to choose a successor for the first pope to resign in over 700 years begins on Tuesday, with the world in suspense over a secret election with no clear frontrunner.

The 115 cardinal electors who will choose the next leader of the world's 1.2 billion Catholics move into a residence inside the Vatican walls where they will sleep and eat for the duration of a conclave expected to last no more than a few days.

The cardinals will be completely cut off -- banned from any communication with the outside world and bound by a strict oath of secrecy on pain of excommunication -- until they have chosen one in their midst to be pope.

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.

Among the possible candidates, three have emerged as clear frontrunners -- 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 many more names in recent days including cardinals from Austria, Hungary, Mexico, the Philippines, South Africa and the United States -- including inspiring pastors and communicators.

The field is wide open but a few key aims unite many of the cardinals after Benedict's troubled eight-year papacy -- reform the intrigue-filled Vatican bureaucracy, counter rising secularism in the West and find new inspiration for Catholics.

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 urgent task 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.

The tradition of holding conclaves goes back to the 13th century when cardinals were locked into the papal palace in Viterbo near Rome by the angry faithful 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, 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 told parishioners that 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 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."

Source: AFP