The 115 voting cardinals are taking part in the second day of the secretive conclave to elect a new pope.
They will have two more opportunities to vote later on Wednesday.
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.
No smoke emerged after the first vote Wednesday morning, meaning the cardinals then entered a second round of voting.
The black smoke that poured from the chimney at 11:39 a.m. local time (6:39 a.m. ET) indicates that no result came from that second ballot either.
The smoke came sooner than expected Wednesday, suggesting the voting is moving swiftly. The cardinals will now go to lunch, when they will be able to talk and mull their options.
The smoke comes from two furnaces set up in the Sistine Chapel especially for the vote. Chemicals are added to make the color of the smoke more obvious.
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.
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.
Black smoke billowed from the chimney of the Sistine Chapel on Tuesday night, after the cardinals failed to choose a new pope in the first day 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.
The secret process got under way earlier Tuesday on a day rich with symbolism as the scarlet-clad cardinals entered the Sistine Chapel in solemn procession, chanting prayers.
Led by the conclave’s senior cardinal, Giovanni Battista Re, each of the cardinal-electors — those under age 80 who are eligible to vote — then swore an oath of secrecy and all those not involved were ordered to leave.
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.
CNN’s Richard Allen Greene reported from Rome and Laura Smith-Spark wrote in London. Ben Brumfield contributed to this report.
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