VATICAN CITY: Pope Francis, hospitalised in critical condition with pneumonia in both lungs, is in a good mood after a peaceful night, the Vatican and a source said Monday, amid global concern over the pontiff's health.

The 88-year-old head of the Catholic Church was admitted to Rome's Gemelli hospital on Feb 14 with breathing difficulties and his condition has since worsened.

But the Vatican's morning bulletin said: "The night passed well, the pope slept and is resting."

Francis "woke up and is continuing his treatment", a Vatican source said.

He was "in a good mood", "can get out of bed", "is not in pain" and was eating "normally", the source said.

The longest hospitalisation of Francis's papacy has brought an outpouring of support for the pope with prayers said around the world and tributes left outside the hospital.

His initial bronchitis developed into double pneumonia and on Saturday the Vatican warned for the first time that the pope's condition was critical.

On Sunday it said Francis continues to receive "high-flow" oxygen through a nasal cannula, and blood tests demonstrated an "initial, mild, renal failure, currently under control."

Francis is alert but "the complexity of the clinical picture, and the need to wait for the pharmacological treatments to have some effect, mean that the prognosis remains reserved," it concluded.

Well-wishers left candles outside the Gemelli hospital, where Francis is in a 10th floor papal suite.

The Vatican was to hold a prayer for the pope in St Peter's Square on Monday.