Black smoke has drifted from the Sistine Chapel’s chimney, signalling that the 115 Roman Catholic cardinals inside have failed to choose a new pope on their first vote.

The cardinals will retire for the evening and meet again tomorrow morning.

They met in the conclave for the first time Tuesday, struggling to choose a new leader after the sudden resignation of Benedict XVI – the first pope to resign in about 600 years.

It’s unknown how long it will take the cardinals to choose a new pope. Some conclaves have lasted mere hours, while the longest – and first conclave – dragged on for nearly three years.

Outside the Sistine Chapel, thousands of faithful Catholics, curious observers and tourists gathered in St. Peter’s Square, watching the chimney and waiting for white smoke – a sign that a pope had been elected.

The cardinals’ secret vote is taking place during a tumultuous time for the Catholic Church, rocked by sex abuse scandals and document leaks that suggest deep divisions among cardinals and other key players at the Vatican.

Before the conclave began Tuesday, retired Cardinal Angelo Sodano, who serves as the dean of the College of Cardinals, urged cardinals to put their differences aside as they vote.

"Each of us is therefore called to co-operate with the Successor of Peter, the visible foundation of such an ecclesial unity," he said.

Canadian Cardinal Marc Ouellet is considered to be among the frontrunners to succeed Benedict XVI, along with Brazilian Cardinal Odilo Scherer and U.S. Cardinal Timothy Dolan.

The cardinals have been meeting informally for over a week to discuss what kind of qualities they want to see in the new pope and what the church’s priorities should be moving forward.

Now that the cardinals are sequestered, some have predicted they will have a tough time agreeing on who should be their new spiritual leader.

The voting takes place in silence and without debate. The cardinals are sealed off from the outside world, prohibited from making phone calls, going online or reading newspapers.

Meanwhile, a group of women who say they have been ordained as priests, defying centuries-old church rules, released pink smoke Tuesday from a balcony overlooking St. Peter’s Square. Among them was Canadian Therese Koturbash, who has been advocating for female clergy.

Various groups have been pushing the issue of women’s ordination, saying it’s time for the Catholic Church to end the discrimination and welcome female priests.

A Ukrainian feminist group, Femen, was also protesting at the Vatican Tuesday and police had to drag two of its topless activists from the edge of St. Peter’s Square.

Among those promising to use St. Peter’s Square as a platform this week is former NBA star Dennis Rodman, who recently travelled to North Korea and praised dictator Kim Jong Un.

Rodman said he will campaign for Ghana’s Cardinal Peter Turkson to become the first black pope.  

With files from The Associated Press