Vatican spokesman Matteo Bruni said cardinals will take part in a solemn mass at St Peter’s Basilica, after which those eligible to vote will gather in the Sistine Chapel for the secretive ballot.

Once they enter the Sistine Chapel, cardinals must have no communication with the outside world until a new Pope is elected.

There is only one round of voting on the first afternoon of the conclave, but the cardinals will vote up to four times every day afterwards.

A new pope requires a two-thirds majority – and that can take time.

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Each cardinal casts his vote on a simple card that says, in Latin: “I elect as Supreme Pontiff” to which they add the name of their chosen candidate.

If the conclave completes its third day without reaching a decision, the cardinals may pause for a day of prayer.

Outside the Sistine Chapel the world will be watching for the smoke from the chimney.

If the smoke is black, there will be another round of voting. White smoke signals that a new pope has been chosen.

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On Saturday, politicians and royalty joined thousands of mourners as Pope Francis’ funeral was held in St Peter’s Square.

Hymns played out on giant speakers, occasionally drowned out by the sound of helicopters flying overhead, before 91-year-old Cardinal Giovanni Battista Re gave a homily on the pope’s legacy.

After a ceremony, huge crowds lined the streets of Rome to watch as the Pope’s coffin was carried in a procession to his final resting place, Santa Maria Maggiore Basilica.