Thousands of faithful gathered in St Peter's Square on Wednesday waiting for smoke to pour from a narrow flue on the roof of the chapel at the end of a day rich in ritual and pageantry, with prelates praying for divine guidance in their secret ballot.
The crowds had to be patient as it took longer than expected for the smoke to appear, more than three hours after the start of the conclave. This was an hour more than it took for smoke to be seen after the first vote in the 2013 conclave that picked the late Pope Francis.
When a pope is chosen, white smoke will emerge, but this had not been expected on Wednesday - a pontiff has not been picked on the first day of a conclave in modern times.
However, some cardinals said this week that they hoped to wrap things up by Thursday or Friday to show the Church can remain unified after the often divisive, 12-year papacy of Francis, who died last month.
The 133 cardinal electors, who are all aged under 80, will spend the night secluded in one of two Vatican guesthouses - where they can continue their deliberations in a more informal setting before returning to the chapel on Thursday morning.
Following Wednesday's single round of voting, the red-hatted "princes of the Church" will hold two votes in the morning session and two in the afternoon, continuing in coming days until one man has secured a majority of at least two-thirds - 89 cardinals this time around.
Their only communication with the outside world will be the smoke from the chimney as they burn their completed ballot papers mixed with special chemicals - black when a voting session ends with no result, white when a pontiff is elected.
Modern papal conclaves are typically short. The 2013 conclave lasted just two days, likewise in 2005 when his predecessor, Benedict XVI, was picked.
In recent days, cardinals have offered different assessments of what they are looking for in the next pontiff who will lead the 1.4-billion-member Church.
While some have called for continuity with Francis' vision of greater openness and reform, others have said they want to turn the clock back and embrace old traditions. Many have indicated they want a more predictable, measured pontificate.
In a sermon ahead of the conclave, Italian Cardinal Giovanni Battista Re, who at 91 is too old to take part in the vote, told his fellow prelates they must set aside "every personal consideration" in choosing the new pontiff and keep in mind "only ... the good of the Church and of humanity".
He also suggested the next pope had to respect diversity within the Church. "Unity does not mean uniformity, but a firm and profound communion in diversity," he said.
No clear favourite has emerged, although Italian Cardinal Pietro Parolin and Filipino Cardinal Luis Antonio Tagle are considered the front-runners.
A record 133 cardinals from 70 countries entered the Sistine Chapel, up from 115 from 48 nations in the last conclave in 2013 - growth that reflects efforts by Francis during his 12-year reign to extend the geographical reach of the Church.
Among their considerations will be whether they should seek a pope from the global South where congregations are growing, as they did in 2013 with Francis, from Argentina, or hand back the reins to Europe, or even pick a first US pope.
Latin chants and organ music accompanied the cardinals as they processed into the frescoed Sistine Chapel before the conclave began. They laid their hands on the Gospels, taking a vow of secrecy not to divulge anything about their gathering.
Archbishop Diego Ravelli, the Vatican's master of ceremonies, then pronounced the Latin command "Extra omnes!" (Everyone out!) telling those not involved in the gathering to leave the room, with the chapel's heavy wooden doors slamming shut on the outside world.
