The Vatican said on Saturday that Pope Francis' health had deteriorated over the past 24 hours and for the first time described his condition as "critical", reporting he had needed supplemental oxygen and blood transfusions.

Doctors on Friday said the 88-year-old Francis is "not out of danger" ​and that the main threat facing him would be the onset of sepsis.

The Vatican said Pope Francis has the "onset of bilateral pneumonia," and that tests, a chest X-ray and the pope's clinical condition present a "complex picture."