Updated 1.30pm

Hundreds of thousands of mourners and world leaders including US President Donald Trump packed St Peter's Square on Saturday for the funeral of Pope Francis, "pope among the people" and the Catholic Church's first Latin American leader.

Some waited overnight to get a seat for the ceremony, with the Vatican reporting some 200,000 people in the square and surrounding streets during the ceremony.

More than 50 heads of state were also present at the solemn ceremony, including Trump -- who met several world leaders in a corner of the basilica beforehand, notably Ukraine's Volodomyr Zelensky, in their first face-to-face since their Oval Office clash in February.

The crowds, packed with young people, applauded as the pope's coffin was carried out of St Peter's Basilica by white gloved pallbearers, accompanied by more than 200 red-robed cardinals.

Francis was "a pope among the people, with an open heart", who strove for a more compassionate, open-minded Catholic Church, Cardinal Giovanni Battista Re said in his funeral homily.

There was applause as he hailed the pope's "conviction that the Church is a home for all, a home with its doors always open".

Francis served as Pope for 12 years, during which time he sought to transform the Church into a more open-minded and inclusive institution.

Guests included Argentina's President Javier Milei and Britain's Prince William as well as Ukraine's Volodymyr Zelensky -- who met Trump on the sidelines, according to a Ukrainian spokesperson.

Some 250,000 people paid their respects before his coffin during its three days of lying in state at St Peter's Basilica, and huge numbers gathered from dawn on Friday to attend his final send-off.

"He was not just the pope, he was what the definition of being human is," said Andrea Ugalde, 39, who flew from Los Angeles to attend Saturday's mass.

"I'm touched by how many people are here. It's beautiful to see all these nationalities together," said Jeremie Metais, 29, from Grenoble, France.

"It's a bit like the centre of the world today."

Italian and Vatican authorities have mounted a major security operation for the ceremony, with more than 50 heads of state on the guest list.

A no-fly zone is in place, fighter jets are on standby and snipers will be positioned on roofs surrounding the tiny city state.

By 6 a.m., the streets and bridges surrounding the Vatican were closed off with rigorous security checks. Within Vatican City alone, around 4,000 police officers have been deployed. To access the funeral mass, attendees must pass through at least three security checkpoints.

An aerial view of St Peter's Square packed with mourners for Pope Francis' funeral. Photo: AFP

"We spent the whole night here in the car with the children," said Peruvian Gabriela Lazo, 41.

"We are very sorry for what happened to him because we hold a South American pope in our hearts."

The funeral sets off the first of nine days of official Vatican mourning for Francis, who took over following the resignation of Pope Benedict XVI in 2013.

After the mourning, cardinals will gather for the conclave to elect a new pope to lead the world's 1.4 billion Catholics.

Diplomatic gathering

Many of Francis's reforms angered traditionalists, while his criticism of injustices, from the treatment of migrants to the damage wrought by global warming, riled many world leaders.

Yet the former archbishop of Buenos Aires's compassion and charisma earned him global affection and respect.

"His gestures and exhortations in favour of refugees and displaced persons are countless," Battista Re said in his homily. 

A reference to Francis’s historic visit to Lampedusa — one of the defining moments of his papacy — was met with particularly strong applause.  The late pope visited the Italian island in 2013 to pray for refugees and migrants lost at sea.

The funeral ceremony featured a range of languages — Latin, English, Italian, French, Arabic, Chinese, Portuguese, and Polish — reflecting the global reach of Pope Francis’s message.

Trump's administration drew the pontiff's ire for its mass deportation of migrants, but the president has paid tribute to "a good man" who "loved the world".

Making the first foreign trip of his second term, Trump sat among dozens of leaders from other countries -- many of them keen to bend his ear over a trade war he unleashed, among other subjects.

A wave of applause rippled through the waiting crowd when Trump was first spotted in St Peter's Square. Minutes later, another round of applause filled the air as the cardinals, dressed in their striking red robes, began their solemn procession.

US President Donald Trump and his wife Melania are escorted to their seats. Photo: Emma Borg

The White House said Saturday that the president had a "very productive" meeting with Ukraine's President Volodymyr Zelensky before the funeral.

Trump's predecessor Joe Biden also attended the funeral, as did presidents Javier Milei of Argentina, Luiz Inacio Lula da Silva of Brazil, France's Emmanuel Macron and Lebanon's Joseph Aoun and many others.

So too did European Commission President Ursula von der Leyen, Britain’s Sir Keir Starmer and more than a dozen members of the UK’s royal family.

Malta's representation

Malta was represented by a sizeable contingent of dignitaries: President Myriam Spiteri Debono, Prime Minister Robert Abela, Opposition Leader Bernard Grech and their spouses, as well as Archbishop Charles Scicluna.

European Parliament President and Maltese MEP Roberta Metsola also attended.

They were joined by hundreds of Maltese youths and priests who originally travelled to Rome for the canonization of Carlo Acutis — often hailed as the first millennial saint. Their pilgrimage has since transformed into a final farewell to Pope Francis.

Israel -- angered by Francis's criticism of its conduct in Gaza -- only sent its Holy See ambassador. China, which does not have formal relations with the Vatican, did not send any representative at all.

In the homily, Battista Re highlighted Francis's incessant calls for peace, and said he urged "reason and honest negotiation" in efforts to end conflicts raging around the world.

"'Build bridges, not walls' was an exhortation he repeated many times," the cardinal said, to an audience that also included Italy's nationalist prime minister, Giorgia Meloni, and Hungary's Viktor Orban.

Atmosphere in St. Peter’s Square

By 8:30 a.m., the choir was in place, rehearsing hymns to ensure perfect pitch and avoid any technical issues during the service.

The square in front of St. Peter’s Basilica was already almost completely packed.

Priests, nuns, and laypeople sat in the front seats, waiting patiently. Behind them, a vibrant sea of flags — including Polish, Colombian, and Lebanese flags — waved in the morning air.

Pallbearers carry the coffin. Photo: AFP

Further back, a sea of neon green — the colour worn by pilgrims during the Jubilee — dominated the view. Many of these younger attendees had initially come to Rome to celebrate the canonization of Acutis but now find themselves participating in a historic farewell.

All entrances to Vatican City were packed, with long lines of people still hoping to gain access.

Simple tomb

Francis died of a stroke and heart failure less than a month after he left hospital where he had battled pneumonia for five weeks.

He loved nothing more than being among his flock, taking selfies with the faithful and kissing babies, and made it his mission to visit the peripheries, rather than mainstream centres of Catholicism.

His last public act, the day before his death, was an Easter Sunday blessing of the entire world, ending his papacy as he had begun it -- with an appeal to protect the "vulnerable, the marginalised and migrants".

The Jesuit chose to be named after Saint Francis of Assisi, saying he wanted "a poor church for the poor", and eschewed fine robes and the papal palace.

Instead, the Church's 266th pope lived at a Vatican guesthouse and chose to be interred in his favourite Rome church, Santa Maria Maggiore -- the first pontiff to be buried outside the Vatican walls in more than a century.

Catholics around the world held events to watch the proceedings live, including in Buenos Aires, where Francis was born Jorge Bergoglio in the poor neighbourhood of Flores in 1936.

"The pope showed us that there was another way to live the faith," said Lara Amado, 25, in the Argentine capital.

Francis asked to be put inside a single wooden coffin to be laid in a simple marble tomb, marked only with the inscription "Franciscus", his name in Latin.

Refusal to judge

Francis's admirers credit him with transforming perceptions of the Church and helping revive the faith following decades of clerical sex abuse scandals.

He was considered a radical by some for allowing divorced believers to receive communion, approving the baptism of transgender believers and blessings for same-sex couples, and refusing to judge gay Catholics.

But he also stuck with some centuries-old dogma, notably holding firm on the Church's opposition to abortion.

Francis strove for "a Church determined to take care of the problems of people and the great anxieties that tear the contemporary world apart", Battista Re said.

"A Church capable of bending down to every person, regardless of their beliefs or condition, and healing their wounds".