Pope Francis, hospitalised for weeks with double pneumonia, continues to improve and the 88-year-old's prognosis is no longer considered uncertain, the Vatican said Monday.

"The clinical conditions of the Holy Father continue to be stable," it said in a statement.

"The improvements recorded in the previous days have been further consolidated, as confirmed by blood tests and clinical objectivity and the good response to pharmacological therapy."

For this reason, they said, doctors had decided to change the prognosis, which had for some time been "reserved" - meaning the outcome was uncertain.

"However, in view of the complexity of the clinical picture and the (pope's) significant infectious picture presented at his hospitalisation, it will be necessary to continue, for further days, the pharmacological medical therapy in a hospital environment," it said.

Francis was admitted to Rome's Gemelli hospital on February 14 with bronchitis, which later turned into pneumonia in both lungs.

He suffered several respiratory crises but has been gradually improving in recent days.