Presidents, royalty and simple mourners bade farewell to Pope Francis on Saturday at a solemn funeral ceremony, where a cardinal appealed for the pontiff's legacy of caring for migrants, the downtrodden and the environment to be kept alive.

U.S. President Donald Trump sat with the rows of foreign dignitaries on one side of Francis' coffin in the vast St. Peter's Square.

On the other side sat cardinals who will pick Francis' successor at a conclave next month, deciding if the new pope should continue with the late pontiff's push for a more open Church or cede to conservatives who want to return to a more traditional papacy.

The Argentine pope, who reigned for 12 years, died at the age of 88 on Monday after suffering a stroke.

"Rich in human warmth and deeply sensitive to today's challenges, Pope Francis truly shared the anxieties, sufferings and hopes of this time," said Italian Cardinal Giovanni Battista Re, who presided over the funeral Mass.

In spiritual language, the 91-year-old Re gave a simple message: there was no going back. The first pontiff from Latin America had been "attentive to the signs of the times and what the Holy Spirit was awakening in the Church," he said.

Francis repeatedly called for an end to conflict during his papacy. His funeral provided an opportunity for Trump, who is pushing for a deal to end Russia's war with Ukraine, to meet Ukrainian President Volodymyr Zelenskiy inside St. Peter's Basilica.

Applause rang out as Francis' coffin, inlaid with a large cross, was brought out of the basilica and into the sun-filled square by 14 white-gloved pallbearers at the start of the Mass.

The Vatican estimated more than 250,000 people attended the ceremony, cramming the square and the roads around.

The crowds clapped loudly again at the end of the service when the ushers picked up the casket and tilted it slightly so more people could see.

Aerial views of the Vatican showed a patchwork of colours - black from the dark garb of the world's leaders, red from the vestments of some 250 cardinals, the purple worn by some of the 400 bishops and the white worn by 4,000 attending priests.

After the funeral, as the great bells of St. Peter's pealed in mourning, the coffin was placed on an open-topped popemobile and driven through the heart of Rome to St. Mary Major Basilica.

Francis, who shunned much of the pomp and privilege of the papacy, had asked to be buried there rather than in St. Peter's -- the first time a pope had been laid to rest outside the Vatican in more than a century.

The burial itself was conducted in private.

The popemobile left the Vatican from the Perugino Gate, a side entrance just yards away from the Santa Marta guesthouse where Francis had chosen to live, instead of the ornate Renaissance apartments in the papal palace.

Crowds estimated by police as numbering some 150,000 lined the 5.5-km (3.4-mile) route to St. Mary Major. The scene resembled many popemobile rides Francis took in his 47 trips to all corners of the world.

Some in the crowd waved signs and others threw flowers towards the casket. They shouted "viva il papa" (long live the pope) and "ciao, Francesco" (goodbye, Francis) as the procession made its way around Rome's ancient monuments, including the Colosseum.

Reuters