Pope Francis, in hospital with pneumonia, is responding well to treatment, the Vatican said on Saturday, adding that the 88-year-old's condition had seen "a gradual, slight improvement".

The Argentine pontiff has been in Rome's Gemelli hospital since February 14, and has suffered several respiratory crises since his admission, but for several days now his condition has been described "stable".

"The Holy Father's clinical condition in recent days has remained stable and, consequently, testifies to a good response to treatment. There is therefore a gradual, slight improvement", the Vatican said.

Though Francis does not have a fever and is "stable", his doctors want the same positive results "in the coming days" before giving a prognosis, the Holy See said in the evening bulletin.

The pope prayed Saturday morning in the chapel belonging to the special papal suite on the hospital's 10th floor, while in the afternoon he alternated rest with work, it said.

The pope has suffered a series of health issues in recent years, from colon surgery in 2021 to a hernia operation in 2023, but this is the longest and most serious hospitalisation of his papacy.