Applause rang out as the coffin, inlaid with a large cross, was brought out of St Peter’s Basilica and into the sun-filled square by 14 white-gloved pallbearers.
Bells tolled as the last of leaders from more than 150 countries took their places.
Dignitaries included US President Donald Trump, who clashed with the pope on numerous occasions over their starkly contrasting positions on immigration.
The open-air ceremony, which was celebrated by 220 cardinals, 750 bishops and more than 4,000 other priests, lasted 90 minutes.
The pope’s casket was placed on a carpet in front of the altar, with the book of gospels laid on top, as the Vatican choirs sang.
Massed ranks of red-robed cardinals sat to one side of the altar, facing rows of black-suited world leaders on the other side.
In front of them were hundreds of priests in white vestments and then thousands of ordinary mourners.
The faithful hurried to the Vatican from the early hours while many camped out to try and secure spots at the front of the crowd for the ceremony.
“We want to say goodbye because he [was a] living saint, very humble and simple,” said Mary James, a Franciscan nun, who had stayed up overnight to guarantee a good place.
The Argentine pope died on Monday, aged 88, following a stroke.
His death ushered in a meticulously planned period of transition for the 1.4-billion member Roman Catholic Church, marked by ancient ritual, pomp and mourning.
Over the past three days, around 250,000 people filed past his body, which was laid out in an open coffin before the altar of the cavernous, 16th-century St. Peter’s Basilica.
Before taking their seats, Trump and his wife Melania paid their respects to Francis’ coffin in St Peter’s Basilica. The coffin was sealed shut on Friday night.
Among the other heads of state who flew into Rome were the presidents of Argentina, France, Gabon, Germany, the Philippines and Poland, together with the prime ministers of Britain and New Zealand, and many European royals.
Applause rang out in the square when Ukraine’s President Volodymyr Zelensky appeared.
Zelensky met Trump while both were in Rome, a spokesman for the Ukrainian leader said, but gave no details.
The Vatican said some 250,000 mourners were expected to fill the vast, cobbled esplanade and access routes to the basilica.
The ceremony was presided over by Cardinal Giovanni Battista Re, a 91-year-old Italian prelate.
“You can feel a lot of energy, yes, a little bit of despair because we are tired, but ultimately we want to come and say ‘thank you’, thanks to Pope Francis for all he did for his church,” said Eduardo Valencia, visiting from Mexico. (Reuters)
