Pope Francis had an "isolated breathing crisis" in hospital on Friday, the Vatican said, in a setback as the 88-year-old pontiff battles double pneumonia.

The Vatican said that the pontiff had pneumonia in both lungs and that he “continued to present a complex picture.”

The death of a sitting pope initiates a profound period of mourning and transition within the Roman Catholic Church, marked by a meticulously structured process to elect a new pontiff