By Alastair Jamieson, Staff writer, NBC News

VATICAN CITY —Black smoke rose above the Sistine Chapel on Tuesday, signaling that 115 Roman Catholic cardinals failed to agree on a new pope during the first day of the papal conclave.

The “princes of the church” began deliberating inside the Vatican after swearing an oath of secrecy and entering the papal conclave at about 5 p.m. local time (12 p.m. ET).

The smoke was created by the burning of ballot papers used by the cardinals in their deciding vote, with chemical cartridges being added to ensure the smoke did not appear to be white — the sign that a decision has been reached. It means the conclave will reconvene on Wednesday morning.

None of the 115 cardinals will be seen or heard, nor will they have any contact with the outside world, until they have chosen a successor to Benedict XVI, who abdicated on Feb. 28.

“They’re on their own now,” said NBC News Vatican expert George Weigel, referring to the total isolation demanded by church rules.

Andrew Medichini / AP

Cardinals from around the world gather in the Vatican to elect the next leader of the Roman Catholic Church.

Shortly after the conclave began, semi-naked feminist activists with the words “pope no more” written on their chests and backs staged a protest right next to St. Peter’s Square, directly in front of the Vatican.

They were tackled by police and detained.

The word “conclave” comes from the Latin meaning “with key”. It is a church tradition that began in 1268 when local officials became so fed up with the lack of a decision among cardinals — they had deliberated for more than two years — that they locked them away with limited food and water to encourage a result.

Earlier, thousands of pilgrims and tourists waited in line to get inside St. Peter’s Basilica for a special pre-conclave Mass with the cardinals.

The “Mass Pro Eligendo Pontifice” began at 10 a.m. local time (5 a.m. ET) in front of a congregation of worshippers who were waiting outside in St. Peter’s Square for tickets allocated on a first-come, first-served basis.

Alastair Jamieson / NBC News

Lois Girten, 55, from Austin, Texas, was among those waiting in line to get inside the pre-conclave Mass.

“It’s in the air! You really feel it,” said Lois Girten, 55, from Austin, Texas, who secured a last-minute place on a two-week pilgrimage to Rome through a cancellation.

“It’s God’s gift that I’m in Rome just as the conclave takes place. I’m almost speechless with excitement, it’s a real treat for me.”

Several thousand visitors were allowed in to take part in the service, according to Religion News Service correspondent Alessandro Speciale inside the basilica.

‘Noble mission’
In his homily, cardinal Angelo Sodano, Dean of the College of Cardinals, told the congregation: “My brothers, let us pray that the Lord will grant us a pontiff who will embrace this noble mission with a generous heart.”

At night, cardinals will walk or be taken by minibus the short distance to the modest rooms in Casa Santa Marta, which John Paul II had built in 1996.

Such is the importance of secrecy that Vatican officials have installed jamming devices to prevent the use of cellphones by cardinals or hidden microphones by anyone wanting to hear their deliberations.

No conclave has lasted more than five days in the past century, with most finishing within two or three days. Pope Benedict was elected within barely 24 hours in 2005 after just four rounds of voting.

Benedict triggered the election last month with his shock decision to abdicate because of his increasingly frail health — the first pontiff to step down in six centuries.

He leaves his successor a sea of troubles — including seemingly never-ending sex-abuse scandals, rivalry and strife inside the Vatican bureaucracy, a shortage of priests and a rise of secularism in its European strongholds.