Pope Francis' health is 'critical,' Vatican says

The health of Pope Francis' has deteriorated over the past 24 hours, the Vatican said in a statement on Saturday, over a week after he was admitted to hospital with breathing difficulties.

"The Holy Father remains alert and has spent the day in a chair, though he is more unwell than yesterday. At the moment, the prognosis remains guarded," the Vatican wrote.

The statement added that the 88-year-old Francis had suffered a "prolonged asthma-like respiratory crisis" that had required blood transfusions.

Doctors had to administer a "high flow" of oxygen because of the pope's breathing crisis, the Vatican said, adding the transfusions were necessary because tests showed that he had a low platelet count, associated with anemia.

Francis 'not out of danger'

"The Holy Father's condition remains critical," the statement continued. "The Pope is not out of danger."

The update, drafted by Francis' medical team but issued by the Vatican, marked the first time the pope's prognosis had been described as "critical," which suggests that it is in flux and requires close observation.

The religious leader was taken to a hospital in Rome a week ago Friday with pneumonia and a complex lung infection.

Double pneumonia can inflame and scar both lungs, making it difficult to breathe.

The Vatican has previously described the pope's infection as "complex," saying it is being caused by two or more micro-organisms.

Professor Sergio Alfieri, who leads the pope's medical team, said Friday that the pontiff's condition was slightly improving, allowing doctors to incrementally lower the amount of medication he is taking.

But he made clear then that the situation was very serious, noting the patient's age and general condition of health.

Earlier on Saturday, the Vatican announced that Francis would not appear in public on Sunday to lead the Angelis prayer with pilgrims. This would make it the second consecutive week he will have missed the event.

Health issues afflict 88-year-old pope

Francis has been head of the Catholic Church since 2013. He has suffered numerous health issues in recent years, including a colon surgery and a hernia operation.

The pope also suffers constant hip and knee pain, which forces him to use a wheelchair most of the time.

This latest illness has cast doubt over his ability to continue as leader of the world's almost 1.4 billion Catholics, fuelling speculation about who might take over.

Vatican Secretary of State Pietro Parolin told Italy's Corriere della Sera daily that such discussion was normal but said he would not enter into "useless speculation."

Before his latest illness, the pope maintained a punishing work schedule, which saw him complete a 12-day tour of the Asia-Pacific in September.