Pope Francis suffered two new episodes of acute respiratory crises and was put back on non-invasive mechanical ventilation, the Vatican has said.

Francis had inhaled “copious” amounts of mucus in another setback in what has become a more than two-week battle to overcome a complex respiratory infection and pneumonia.

In a late update on Monday, the Vatican said the episodes were caused by a “significant accumulation” of mucus in his lungs and bronchial spasms.

A man walks in the ward where Pope Francis is being treated at the Agostino Gemelli Polyclinic in Rome (Andrew Medichini/AP)

“Two bronchoscopies were performed with the need for aspiration of copious secretions,” the Vatican said.

Francis remained alert, oriented and has co-operated with medical personnel.

The prognosis remained guarded.