Cardinals hold a mass at St. Peter's Basilica ahead of their conclave, where they will be locked up inside the Sistine Chapel until they choose a new pope.
About a dozen names have often been mentioned as frontrunners.
And in the Philippines, Asia's largest Catholic nation -- the faithful are rallying behind one candidate seen as a dark horse -- their own Cardinal Luis Antonio Tagle.
Tagle has attracted 128,000 likes on his Facebook page, where videos of his weekly television show are posted.
Supporters on- and offline say Tagle will be able to address issues like alleged sexual abuse by priests, and the waning numbers of Catholics among the young.
(SOUNDBITE) (English) EXECUTIVE DIRECTOR OF JESUIT COMMUNICATIONS, EMMANUEL ALFONSO, SAYING:
"If ever he becomes pope, what will he be bringing to the church leadership? And precisely this -- the energy, the energy to engage the young people, the energy to speak their language, the energy to listen to them
