Vatican City, Holy See (AFP)-Cardinals prepared to cast fresh votes Thursday for the next head of the Catholic Church, after sending up a second round of black smoke to signal they had again failed to elect a pope.

The 133 cardinals began their secretive conclave in the 15th-century Sistine Chapel on Wednesday afternoon, seeking a successor to Pope Francis as head of the world’s 1.4 billion Catholics.

Since then, they have twice sent up black smoke, the latest at Thursday lunchtime, to let the world know that no one had yet secured the two-thirds majority required to be elected pontiff.

The centuries-old ritual is held entirely behind closed doors but the red-robed cardinals were scheduled to have two votes on Thursday afternoon after lunch at the Santa Marta guesthouse, where they are staying.

Sworn to secrecy, their only method of communication is by burning their ballot papers to send up smoke through the chapel chimney — coloured black if they have no decision, white for a new pope.

Among the thousands of Catholics and curious tourists gathered in St Peter’s Square to watch the proceedings, there was some disappointment earlier, but others said they were happy to wait.

Emmanuel Quiros Chavarria, 34, a Costa Rican priest studying in Rome, told AFP it was a good sign the cardinals were not rushing — even if he hoped to see white smoke on Thursday afternoon.

“The most important thing is that the elected pope is a man of unity and balance,” he said.

– Take your time –

On Wednesday, the first day of the conclave, the black smoke came some three hours and 15 minutes after the cardinals closed the doors of the Sistine Chapel.

If no pope emerges in the two votes to come Thursday afternoon, the voting will continue Friday — and for as long as it takes to find consensus.

In 2005, Pope Benedict XVI was elected in four ballots over two days and Pope Francis in 2013 in five ballots over two days.

“I don’t want it rushed — whatever they need to do to make the right decision,” said Barbara Mason, 50, who travelled from Canada for the conclave.

A central question is whether cardinals will choose someone in the image of Francis — who defended the poor, migrants and marginalised around the globe — or someone more focused on defending Church doctrine.

The charismatic Argentine reformer died on April 21, aged 88.

“I’d like someone moderately conservative,” one French pilgrim in the crowd who gave his name as Augustin told AFP.

“The church needs unity and strong values,” said the 24-year-old, who arrived at the Vatican after travelling on foot from a Tuscan monastery.

But US tourist Colter Sikora said he worried the faith could become “smaller or more niche” despite its responsibility “for serving a lot of people.

“You want somebody who’s holy, but has, like Francis, a little bit of charisma, somebody that you look up to and want to follow as a leader,” said the 37-year-old.