On Wednesday (early Thursday AEST), the cardinals in their red robes entered the Sistine Chapel in pairs, chanting the solemn Litany of the Saints as Swiss Guards stood watch.

Cardinal Pietro Parolin, who served as the secretary of state under Francis and is a prominent candidate to become the next pope, took charge of the proceedings as the senior cardinal under 80 years old eligible to join the conclave.

Speaking in Latin, Parolin stood before Michelangelo’s vision of heaven and hell, The Last Judgment, and led the cardinals in a lengthy oath.

Each one followed, placing his hand on the Gospel and promising in Latin to maintain utmost secrecy.

The stirring ritual, filled with vibrant colors, chants, incense, and gravity, was more captivating than anything Hollywood could portray, highlighting the importance of the occasion.

Outside in St Peter’s Square, hundreds of people watched the proceedings on giant video screens until the Vatican feed cut off.

Hailing from 70 countries, the cardinals have been sequestered from the outside world, their cellphones surrendered and airwaves around the Vatican jammed to prevent all communications until they find a new pope.

Francis named 108 of the 133 “princes of the church”, choosing many pastors in his image from far-flung countries like Mongolia, Sweden and Tonga that had never had a cardinal before.

His decision to surpass the usual limit of 120 cardinal electors and include younger ones from the “global south” — often marginalised countries with lower economic clout — has injected an unusual degree of uncertainty in a process that is always full of mystery and suspense, with smoke signals telling the world if a pope has been elected or not.

Many cardinals hadn’t met until last week and lamented they needed more time to get to know one another, raising questions about how long it might take for one man to secure the two-thirds majority, or 89 ballots, necessary to become the 267th pope.

“Wait and see, a little patience, wait and see,” said Cardinal Mario Zenari, the Vatican’s ambassador to Syria.

A final Mass, then ‘All out’

Earlier in the day, the dean of the College of Cardinals, Cardinal Giovanni Battista Re, presided over a morning Mass in St Peter’s Basilica urging the voters to set aside all personal interests and find a pope who prizes unity. The world today needs a leader who can awaken consciences, he said.

“Let us pray that God will grant the church a pope who knows how best to awaken the consciences of all and the moral and spiritual energies in today’s society,” Re said.

He reminded them that the awesomeness of the Sistine Chapel’s frescoes, and Michelangelo’s in particular, is meant to remind the cardinals of the weighty responsibility they bear.

In his regulations for the conclave, St John Paul II wrote that in the Sistine Chapel, “everything is conducive to an awareness of the presence of God”.

After the cardinals took their oaths, the master of papal liturgical ceremonies, Archbishop Diego Ravelli, called out “Extra omnes” and anyone not eligible to vote left before the chapel doors closed. An elderly cardinal remained to deliver a meditation, but after it was finished he, too, had to leave.

The cardinals don’t have to take a first vote Wednesday, but they are expected to. Assuming no winner is found, the Vatican said black smoke could be expected out of the Sistine Chapel chimney about 7pm (3am AEST).

The cardinals retire for the night and return Thursday morning. They can hold up to two ballots in the morning and two in the afternoon until a winner is found.

While cardinals this week said they expected a short conclave, it will likely take at least a few rounds of voting. For much of the past century, it has taken between three and 14 ballots to find a pope.

John Paul I — the pope who reigned for 33 days in 1978 — was elected on the fourth ballot. His successor, John Paul II, needed eight. Francis was elected on the fifth in 2013.

Lobbying before the conclave

While the cardinals are supposed to resist any “secular” influences in their choice, such lobbying abounded in Rome in the days before the conclave as various groups reminded cardinals of what ordinary Catholics want in a leader.

Young Catholics penned an open letter reminding cardinals that there is no church without young people, women and the laity. Conservative Catholic media slipped cardinals copies of a glossy book containing their assessments of contenders. Survivors of clergy sexual abuse warned cardinals that they would be held accountable if they failed to find a leader who will crack down on decades of abuse and cover-up.

Advocates for women’s ordination were sending pink smoke signals over the Vatican to demand that women be allowed to be priests and participate in a conclave.

Even the White House got involved, posting a photo of President Donald Trump dressed as a pope. Trump said it was a joke, but the gesture was denounced by former Italian Premier Romano Prodi as “indecent” political interference in matters of faith that harked back to times when secular rulers habitually wielded religion to stay in power.

Lisette Herrera, a 54-year-old tourist from the Dominican Republic, was deeply moved to find herself by chance in Rome as the conclave began. She decided Wednesday morning to skip the Spanish Steps and Trevi Fountain and pray instead in St Peter’s Square.

“I’m praying to the Holy Spirit for a young pope who would stay with us for a long time,” she said. “I don’t believe in conclave politics, I just feel that the Holy Spirit is here and that’s all we need to know.”

Armando Statti, a pilgrim from Crotone, Italy, said he expected cardinals would settle on a pope in the image of Francis or John Paul II.

“We hope he will be announced as soon as possible, for the sake of the whole world and for peace, and that he will embrace everyone,” he said.

Challenges facing a new pope

Many challenges face the new pope and weigh on the cardinals — above all whether to continue and consolidate Francis’ progressive legacy on promoting women, LGBTQ+ acceptance, the environment and migrants, or roll it back to try to unify a church that became more polarized during his pontificate. The clergy sex abuse scandal hung over the pre-conclave talks.

Since Francis chose 80 per cent of the voters, continuity is likely, but the form it might take is uncertain and identifying front-runners has been a challenge.

But some names keep appearing on lists of “papabile,” or cardinals having the qualities to be pope.

— Cardinal Pietro Parolin, 70, an Italian who was Francis’ secretary of state and the Vatican No. 2, is a leading contender.

— Filipino Cardinal Luis Tagle, 67, is a top candidate to be history’s first Asian pope. He had a similarly high-profile job, heading the Vatican’s evangelization office responsible for the Catholic Church in much of the developing world.

— Hungarian Cardinal Peter Erdo, 72, the archbishop of Budapest, is a leading candidate representing the more conservative wing of the church.