As Pope Francis has battled double pneumonia in hospital for nearly three weeks, talk of the 88-year-old pontiff's death or resignation has become almost commonplace.

Pope Francis suffered two episodes of acute respiratory failure Monday, the Vatican said, a fresh setback in the worst health crisis of his papacy.

Pope Francis had stabilised enough on Tuesday after two respiratory crises to be taken off non-invasive mechanical ventilation and resume receiving just high flows of supplemental oxygen via a nasal tube to help him breathe,