The 88-year-old has pneumonia in both lungs and remains in a critical condition despite showing a slight improvement after 11 days in the hospital. The Vatican said early on Tuesday (Tuesday night AEDT) that he had “slept well, all night”.

Still, the mood was mostly grim in the monumental square, with many of the roughly 4000 assembled understanding they may be in Rome for Francis’ final days. Crowds sat under umbrellas on folding chairs or stood by the vast colonnades as they reflected fondly on the pontiff’s legacy.

“To see him suffer hurts,” said Robert Pietro, a Romanian seminarian who stood at the prayer holding a small, fragrant candle in tribute.

“But we also pray in thanksgiving for what he has done for the church.”

The Reverend Roberto Allison, a priest from Guadalajara, Mexico, said members of his community had come together to show appreciation for “all that we have learned from him”.

Stopping to deliver personal blessings to some at the end of the ceremony, Cardinal Angelo Bagnasco said the crowd’s diversity — many world languages could be heard spoken — was “a big sign of comfort” for the Catholic Church.

The Argentine pope, who had part of one lung removed as a young man, has been hospitalised at Rome’s Gemelli hospital since February 14 and doctors have said his condition is touch-and-go, given his age, fragility and preexisting lung disease.

But in Monday’s update, they said he hadn’t had any more respiratory crises since Saturday, and the supplemental oxygen he is using continued but with a slightly reduced oxygen flow and concentrations.

A couple of Catholic tourists from Chicago, who arrived holding umbrellas well before the service started, said they prayed for the pope at daily Mass earlier at St Peter’s Basilica, and decided to come back. Like many, they found it “hard to process” they may be in Rome for Francis’ final days.

“No one knows the day and time, but it’s a historic moment nonetheless,” said Edward Burjek.

It felt the same for Hatzumi Villanueva of Peru. She was particularly fond of former pope St John Paul II but said that Francis, as the first Latin American pope, “draws a bit closer”.

“We came to pray for the pope, that he may recover soon, for the great mission he’s sharing with his message of peace,” said Villanueva, who praised his empathy for migrants.

Francis’ papacy has also emphasised the defence of the environment and partial openness to LGBTQ+ rights.

Outside of the Vatican, Romans, pilgrims and even non-Catholics said they were offering special prayers for the hospitalised pope.

“We are all sorry,” said Raniero Mancinelli, who has tailored ceremonial clothing for Francis and the two previous popes in his shop just outside the Vatican’s walls.

Elisabetta Zumbo carried a 1.5-metre-long cross down a cordoned-off section of the street leading to St Peter’s as she prepared to lead a group of 34 pilgrims from the northern Italian city of Piacenza. With the rain pouring down, she pledged her group would pray intensely for the pope.

“There is a lot of emotion and a lot of sadness,” Zumbo said.

Nearby, a couple from London visiting St Peter’s with their son said that even though they’re not Catholic, they felt close to the pontiff “being there in his home” in the monumental basilica.