Cardinals at the Vatican have retreated into the Sistine Chapel for a conclave to elect a new Roman Catholic pope after celebrating a church service.
A few hours after the gathering began, black smoke rose from the chimney above the chapel, signaling that a first vote had failed.
Ahead of the conclave, Cardinal Angelo Sodano, dean of the College of Cardinals, called for unity within the Roman Catholic Church.
The 115 cardinals from 48 countries will cast secret ballots to pick the church's 266th pope.
The voting could go on for days.
Italy's Angelo Scola and Brazil's Odilo Scherer were both seen as strong candidates to secure the 77 votes needed for victory.
The cardinals' ballots will be burned to give the public a glimpse of how the voting is going. White smoke rising from the chimney above the chapel means a victor has emerged, while black smoke means an indecisive vote.
The conclave comes a month after Pope Benedict XVI shocked the church's 1.2 billion faithful by becoming the first pontiff in 600 years to resign after eight years as head of the church.
The new pope faces problems, including sex scandals and falling membership.
The 63-year-old Scherer is the leading candidate from Latin America, where 42 percent of the world's Catholics live.
Scherer would be the first non-European pope in 1,300 years.
While described as a conservative, Scherer has embraced new technologies, including Twitter messaging.
"What we have to face right now is the coming together of consequences of a culture that has expanded very quickly in light of the new conditions for communication and the spreading of all forms of cultural expression, and this is a very big challenge we are facing right now," Scherer said in a recent interview.
Analysts say Scherer appears to have the backing of the Vatican bureaucracy called the Curia.
Scola, on the other hand, is reportedly favored by cardinals hoping to shake up the powerful Curia.
Analysts say, however, the longer the voting drags on the more unpredictable things could become.
And that could raise the chances of other leading candidates, including Canada's Marc Ouellet, the U.S. cardinals Sean O'Malley and Timothy Dolan, as well as Argentina's Leonardo Sandri.
With reporting by AP and Reuters