Catholics around the world are marking the 12th anniversary of Pope Francis's election as pontiff by praying for his recovery.

Francis, who was elected on 13 March 2013, has been in Rome's Gemelli hospital for almost a month. He is being treated for double pneumonia and other infections, and has suffered several respiratory crises, which raised concerns about his survival.

The latest bulletins from the Vatican have said the 88-year-old is stable after a chest X-ray confirmed "improvements" in his condition in recent days.

But they said his condition was still complex and that he required further hospital treatment. It is not clear when he will be allowed to leave.

"The clinical condition of the Holy Father has remained stable in the context of an overall complex medical picture," according to a statement published by Vatican News.

"The chest X-ray performed [on Tuesday] has radiologically confirmed the improvements observed in the previous days," it said.

The Pope has not been seen in public since his admission to hospital and no photographs have been released.

But earlier this month, an audio recording of him speaking in his native Spanish was played in St Peter's Square in Vatican City.

His voice, as he thanked the faithful for their rosary prayers for his health, was breathless and weak.

In recent days, the Pope has joined spiritual exercises of prayers and meditation held at the Vatican via video link, without being seen.

In a break with tradition, the Holy See has provided daily updates at Francis's own request.

He has been receiving non-invasive oxygen therapy, administered by nasal tubes during the day and via a mask at night.

His illness has changed the tenor of the way Catholics are celebrating his anniversary.

Cardinal Michael Czerny, a senior Vatican official known to be close to Francis, called the occasion "a reason for gratitude".

"This year, his illness makes us especially grateful to God… redoubling our prayers for his full recovery," the Cardinal said.

Francis, born Jorge Mario Bergoglio, is the first pope from the Americas.

In his native Argentina, churches across the country will hold masses of thanksgiving to mark the anniversary. The services will also include prayers for his health.

Father Claudio, who was visiting St Peter's Square from Angola, said: "The situation that we find the Holy Father in, that he is so ill, truly it is a very great worry at this moment."

He added: "We're praying for the Holy Father that he is returned to full health."

Arianna, a student from Piacenza in Italy, said she was "really happy" that the Pope was getting better.

"I was really upset when I heard he was ill, because he's a very important figure for everyone. I was really concerned about him."

The Pope, who has been known to work himself to exhaustion, is likely to face a long road to recovery.

There has been speculation that he could choose to follow his predecessor Benedict XVI and resign the papacy. But his friends and biographers have insisted he has no plans to step down.

2025 is a Catholic Holy Year, with 32 million pilgrims expected to come to Rome.

Francis has also been planning at least one foreign trip to Turkey for the celebration of the 1,700th anniversary of a major Christian council of bishops in ancient Nicaea.

Despite his fragile health, he has continued his work from hospital.

"Happy anniversary, Pope Francis," the Italian Catholic writer Andrea Tornielli wrote on Vatican News.

"We look with affection and hope at the windows of the 10th floor of Gemelli Hospital," he said.

He thanked Pope Francis for "that still feeble voice of his that has joined the Rosary in St Peter's Square in recent days - a fragile voice that continues to implore peace and not war, dialogue and not oppression, compassion and not indifference."

"We still need your voice so much," he said.