Thick black smoke billowed into the night sky from the Sistine Chapel's chimney tonight, signalling an inconclusive first vote in the conclave to elect a new pope.
Thousands of faithful huddled in St. Peter's Square to watch the smoke pour out of the narrow flue in the rain-laden gloom following a day rich in ritual and pageantry.
After praying for divine guidance, the red-hatted cardinals took a solemn vow, in Latin, never to divulge any details of their deliberations. They then secluded themselves behind the chapel's heavy wooden doors.
No conclave in the modern era has chosen a pope on its first day, and some cardinals speculated this week that it might take four or five days to pick the man to replace Pope Benedict, who unexpectedly abdicated last month.
The so-called "Princes of the Church" will spend the night in a Vatican hotel before returning to the frescoed Sistine Chapel tomorrow to continue their votes, with two rounds set for the morning and two for the afternoon.
Until they chose a new pontiff, their only communication with the outside world will be the smoke from the Chapel chimney - black when voting sessions end with no result and white when a pontiff is elected.
Whoever becomes the 266th pontiff in the Church's 2,000-year history will face a daunting array of problems, including sex abuse scandals, infighting within the Vatican bureaucracy and the spread of secularism in its European heartland and beyond.
No clear-cut front runner has emerged, with some prelates pushing for a strong manager to control the much criticised central administration, known as the Curia, while others want a powerful pastor to promote their faith across the globe.
Italy's Angelo Scola and Brazil's Odilo Scherer are spoken of as strong contenders. The former would return the papacy to Italy after 35 years in the hands of Poland's John Paul II and the German Benedict XVI.
Scherer would be the first non-European pope since Syrian-born Gregory III in the 8th century. However, a host of other candidates have also been mentioned as "papabili" - potential popes - including U.S. cardinals Timothy Dolan and Sean O'Malley, Canada's Marc Ouellet and Argentina's Leonardo Sandri.
Latin chants accompanied the cardinals as they processed into the Sistine Chapel earlier, with Michelangelo's depiction of Christ delivering the Last Judgment on the back wall and his image of the hand of God giving life to Adam on the ceiling.
The doors were shut at 5.34 pm (4.34pm Irish time) after the master of ceremonies, Guido Marini, said "Extra Omnes" (Latin for "Everyone Out"), asking all those not associated with the gathering to leave the room.
Maltese Cardinal Prosper Grech, who at 87 is too old to participate in the voting, remained inside to give a sermon to remind the 115 cardinal electors of the gravity of their responsibility.