Black smoke poured from the chimney fixed to the roof of the Sistine Chapel on Wednesday morning, indicating that the cardinals' first two votes of the day were inconclusive.
The 115 voting cardinals are taking part in the second day of the secretive conclave to elect a new pope.
After a lunch break, the cardinals returned to the Sistine Chapel, famed for its frescoes by Michelangelo, for another round of balloting.
Outside, all eyes turned again to the chimney on the chapel roof as the world awaits the outcome of the closed-door election.
If the cardinals elect a new pope with the afternoon first ballot, white smoke could billow forth around 5:30 p.m. (12:30 p.m. ET.)
If no pope is elected they will vote once more Wednesday evening. If no result comes at that time, another puff of black smoke will be sent up.
Three ballots have been held so far in total, all inconclusive.
A two-thirds majority is required to confirm a new pontiff to step into the shoes left empty by the historic resignation of Benedict XVI at the end of last month.
Whoever it may be will take on the leadership of a church that has been rocked by child sex abuse scandals and corruption claims in recent years.
White or black smoke?
The black smoke that poured from the chimney at 11:39 a.m. indicated that no result came from the two votes held Wednesday morning.
The smoke came somewhat earlier in the day than expected because once the cardinals are familiar with the voting procedures, they can move relatively quickly, according to the Rev. Thomas Rosica, a Vatican spokesman.
However, that does not mean they are moving rapidly toward a decisive vote.
After the two morning ballots, the cardinals went to lunch in the Vatican hotel where they are staying.
While away from the Sistine Chapel, they are able to have informal conversations and mull their options before voting again.
Vatican spokesman the Rev. Federico Lombardi told reporters that the inconclusive results so far were not unexpected, based on the number of ballots held in past conclaves.
Rosica added, "This is normal and one should not interpret this as division amongst the cardinals."
In response to a question about criticism leveled against some cardinals by a group representing the victims of clerical sex abuse, the Survivors Network of Those Abused by Priests, the Vatican spokesmen defended their right to take part in the conclave.
"We are very well aware of SNAP and their activities," Rosica said. "SNAP have chosen this event to amplify their activities."
The cardinals named by SNAP "are worthy of our esteem," he said.
Last week, SNAP released its "Dirty Dozen" list of men it judged would be the worst candidates for pope because of their handling of, or comments on, past allegations of child sex abuse against clergy.
In one high-profile case, four California men who alleged clerical sex abuse have settled their lawsuits against their former priest, the Los Angeles Archdiocese and Cardinal Roger Mahony for almost $10 million, their attorneys said Tuesday.
In the run-up to the conclave, victims' groups called on Mahony not to take part because of his handling of the abuse scandal.
Tod Tamberg, a spokesman for Mahony, said the allegations predated his time as archbishop.
The emergence of such sex abuse scandals has shaken global confidence in the church in recent years, and dealing with the issue effectively is sure to be a priority for the new pope.
Peal of Vatican bells
The cardinals will conduct four votes a day for three days, Lombardi said, with a break likely on Saturday if no one has been elected by then. The day's pause would allow the cardinals time for further discussions before they cast their ballots again.
Two stoves are set up in the Sistine Chapel especially for the votes. The ballots are burned in one, while special cartridges containing a mix of chemicals are released in the other to make the color of the smoke more obvious, either black or white, Rosica said.
The cartridges produce smoke for about seven minutes, he said.
If a pope has been elected, the cardinals burn the ballots immediately. If not, the cardinals hold on to them and proceed to a second round of voting.
They burn the ballots from both rounds together after the second round.
In the past, discerning the color has been difficult at times, as it has appeared gray. But there is a second, unmistakable sign: If the smoke is indeed white, the Vatican church bells ring to celebrate the choice.
This can happen after a short delay, as was the case when the white smoke went up to signal the election of Benedict XVI.
In any case, the wait for the announcement of a new church leader should not be too long. The longest papal conclave in the past century took just five days.
If a new pope is in place by Sunday, he would probably lead the Angelus prayers on that day, Lombardi said. The first public Mass would be the inauguration Mass.
Black smoke also billowed from the chimney of the Sistine Chapel on Tuesday night, after the cardinals failed to choose a new pope in the first vote of their conclave.
Huddled under umbrellas as rain came down, crowds of onlookers watched the chimney and big screens set up in St. Peter's Square.
Filipino priest and CNN iReporter Joel Camaya was among a number of Catholic faithful in the square who watched as the black smoke poured out.
There was "a collective sigh of disappointment and everyone started heading home," he said. "There was no pope, yet."
The public interest reflects the "very intense and beautiful period" the church is experiencing at the moment, Lombardi said. "We are feeling the level of intensity of the wait. We saw many people in the square last night, a lot more than I myself had expected."
Pope emeritus Benedict XVI also watched on television as the black smoke rose on Tuesday, Lombardi said.
Benedict had earlier watched on TV as the scarlet-clad cardinals attended a special Mass and took their oath of secrecy in the Sistine Chapel to begin the conclave to elect his successor, he said.
The Vatican received calls Tuesday night from people concerned that the heavy black smoke might have caused damage to the Sistine Chapel or created problems for the cardinals, Rosica said.
But, he said, he could confirm that the frescoes have not been damaged and that the cardinals are enjoying good health.
The cardinals will remain locked in isolation until one candidate, almost certainly from among their number, garners a two-thirds majority, or 77 votes, and is named the new spiritual head of the world's 1.2 billion Roman Catholics.
Until that moment, the cardinals are barred from communicating with the outside world in any way. Jamming devices have been installed to prevent the use of cell phones or other devices.
The cardinals stay in the Casa Santa Marta, a Vatican City hotel, for the duration of the conclave, moving from there to the Pauline Chapel to pray or the Sistine Chapel to vote.
Applause echoed around St. Peter's Basilica on Tuesday as Cardinal Angelo Sodano, dean of the College of Cardinals, offered thanks for the "brilliant pontificate" of Benedict, whose unexpected resignation precipitated the selection of a new pope.
When cardinals elected Benedict in 2005, after a conclave that ran into a second day, the white smoke signaling the decision came about six hours after an earlier, inconclusive vote.
Benedict is currently staying at the summer papal residence, Castel Gandolfo, while restoration work is carried out on a small monastery within Vatican City. Once it is ready, he will live out his days there in study and prayer.
-- CNN's Richard Allen Greene and Hada Messia reported from Rome and Laura Smith-Spark wrote in London. CNN's Ben Brumfield and Stephen Howie contributed to this report.
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