More clinical tests were being performed on the 88-year-old pope, who had part of one lung removed as a young man.

Pope Francis, who is battling double pneumonia in hospital, had a "tranquil" night and rested, the Vatican said on Sunday. It comes after news that the Pope's health had deteriorated over the past 24 hours.

Pope Francis was in critical condition Saturday after he suffered a long asthmatic respiratory crisis that required high flows of oxygen, the Vatican said.