On Sunday it said Francis continues to receive “high-flow” oxygen through a nasal cannula, and blood tests demonstrated an “initial, mild, renal failure, currently under control”.

Francis is alert but “the complexity of the clinical picture, and the need to wait for the pharmacological treatments to have some effect, mean that the prognosis remains reserved,” it concluded.

Well-wishers have left candles outside the Gemelli hospital, where Francis is in a special papal suite on the 10th floor, and where the Vatican said he took part in a mass on Sunday morning.

Abele Donati, head of the anaesthesia and intensive care unit at the Marche University Hospital, told the Corriere della Sera daily that the renal failure “could signal the presence of sepsis in the early stages”.

“It is the body’s response to an ongoing infection, in this case of the two lungs”, he said.

Professor Sergio Alfieri, leading the Gemelli medical team treating the pope, warned at a press conference on Friday that “the real risk in these cases is that the germs pass into the blood”, which could result in sepsis, a life-threatening condition.

‘Need his figure’

Francis’s hospitalisation has sparked widespread concern and fears over the pope’s recovery.

“At this moment in history, one feels the need for his figure”, Jesuit theologian Antonio Spadaro, who is close to Francis, told the Repubblica daily on Monday.

There were “many people around the world, including those in positions of responsibility, who are genuinely concerned because they know that Francis is one of the few who is able to connect the dots in a world that seems to be split”, he said.

The condition of the pope, who had part of one of his lungs removed as a young man, has fuelled speculation about whether he might recover but then resign.

He has always left the door open to following his predecessor, Benedict XVI, who in 2013 became the first pope since the Middle Ages to step down because of his physical and mental health.

But Francis has repeatedly said it was not the time.

Spadaro agreed, saying “this is not the time to talk about the so-called resignation”.

“The pope is vigilant, he is exercising his pastoral duty even from his hospital bed, and – although in a different, less visible manner – he manifests his presence”, he said.

German Cardinal Gerhard Ludwig Muller told the Corriere della Sera “the pope is alive and this is the moment to pray, not think about his successor”.

But had added: “We all must die. There is no eternal earthly life. The pope has a special task, but he is a man like all men”.