Vatican City - With Pope Francis laid to rest, all eyes turn now to the conclave, the secretive meeting of cardinals set to convene within days to elect a new head of the Catholic Church.

Alongside world leaders and reigning monarchs, an estimated 400,000 people turned out on Saturday for the Argentine pontiff's funeral at the Vatican and burial in Rome.

The crowds were a testament to the popularity of Francis, an energetic reformer who championed the poorest and most vulnerable.

Many of those mourning the late pope, who died on Monday aged 88, expressed anxiety about who would succeed him.

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"He ended up transforming the Church into something more normal, more human," said Romina Cacciatore (48), an Argentinian translator living in Italy. "I'm worried about what's coming."

On Monday morning, at 9:00 AM, cardinals will hold their fifth general meeting since the pope's death, at which they are expected to announce a date for the conclave.

Held behind locked doors in the frescoed Sistine Chapel, the election of a pope has been a subject of public fascination for centuries.

Cardinal-electors will cast four votes a day until one candidate secures a two-thirds majority, a result broadcast to the waiting world by burning papers that emit white smoke.

Luxembourg Cardinal Jean-Claude Hollerich said last week he expected the conclave to take place on May 5 or 6 – shortly after the nine days of papal mourning, which ends on May 4.

German Cardinal Reinhard Marx told reporters Saturday the conclave would last just "a few days."

Francis' funeral was held in St. Peter's Square in bright spring sunshine, a mix of solemn ceremony and an outpouring of emotion for the Church's first Latin American pope.

More crowds are expected on Sunday when the public can begin visiting his simple marble tomb at the basilica of Santa Maria Maggiore, his favorite church in Rome.

Francis was buried in an alcove of the church, becoming the first pope in more than a century to be interred outside the Vatican.

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In his homily at the funeral, Cardinal Giovanni Battista Re highlighted the Jesuit's defense of migrants, relentless calls for peace, and belief that the Church was a "home for all."

Many of the mourners expressed hope that the next pope would follow his example, at a time of widespread global conflict and growing right-wing populism.

"We are concerned; hopefully the pope will carry on the foundations left by Pope Francis," said Evelyn Villalta, a 74-year-old from Guatemala.

"He was a pope who left his mark on our generation," added Marine De Parcevaux, a 21-year-old French student who attended the mass.

Marx said the debate over the next pope was open, adding: "It's not a question of being conservative or progressive... the new pope must have a universal vision."

More than 220 of the Church's 252 cardinals were at Saturday's funeral, and will gather again on Sunday afternoon at Santa Maria Maggiore to pay their respects at Francis' tomb.

There will also be a mass at St. Peter's Basilica at 10:30 AM on Sunday, led by Pietro Parolin, who was secretary of state under Francis and is a front-runner to become the next pope.

Only cardinals under the age of 80 are eligible to vote in the conclave, with 135 currently eligible – most of whom Francis appointed himself.

But experts caution against assuming they will choose someone like him.

Francis, a former archbishop of Buenos Aires who loved being among his flock, was a very different character to his predecessor Benedict XVI, a German theologian better suited to books than kissing babies.

Benedict, in turn, was a marked change from his Polish predecessor, the charismatic, athletic, and hugely popular John Paul II.

Francis' changes triggered anger among many conservative Catholics, and many of them are hoping the next pope will turn the focus back on doctrine.

Some cardinals have admitted the weight of the responsibility that faces them in choosing a new head of the world's 1.4 billion Catholics.

"We feel very small," Hollerich said last week. "We have to make decisions for the whole Church, so we really need to pray for ourselves."