Vatican City, Holy See: 

"The clinical conditions of the Holy Father are confirmed to be improving today also," said the Vatican in an evening bulletin on the pope's health.

 Pope Francis's condition was continuing to improve, the Vatican said Thursday, as the 88-year-old pontiff marked two weeks in the hospital with pneumonia in both lungs.It was the second consecutive day the Vatican cited an improvement in the critical condition of the Argentine pope, who was admitted to Rome's Gemelli hospital on February 14.

As pilgrims and other well-wishers continue to gather to pray and leave offerings outside the hospital, medical experts -- together with the Vatican -- have warned that Francis is not out of danger.

"Given the complexity of the clinical picture, further days of clinical stability are necessary to resolve the prognosis," the Vatican statement said.

After first being admitted to the hospital with breathing difficulties, the Vatican revealed that the pope -- who had part of a lung removed as a young man -- had double pneumonia. But on Wednesday, it said that Francis's clinical conditions had shown a "slight improvement" while cautioning that his prognosis remained "reserved".

The respiratory attack Francis suffered at the weekend that required high levels of oxygen has not been repeated, although he continues to receive oxygen and do breathing exercises.

On Thursday, he "alternated high-flow oxygen therapy with a venturi mask," the Vatican said, referring to an oxygen mask that delivers oxygen at controlled concentrations.

"In the morning, the Holy Father dedicated his time to respiratory physiotherapy, alternating it with rest," said the Vatican.

He then spent time working, it said. The pope's latest improvement comes after his deteriorating condition at the weekend sparked fears that the head of the world's nearly 1.4 billion Catholics might not pull through.

In the afternoon, following another session of therapy he prayed in the chapel located on the 10th floor of the Gemelli in the special papal suite, said the Vatican.

"Today we go back to Mexico and we wanted before we leave to come and see where he is. It doesn't matter if we only see the window, but we also wanted to say some prayers," a teary Lili Iparrea Fernandez, 74, told AFP.

Doctors have warned the path to recovery could be long, with the Jesuit pontiff likely staying in hospital beyond this week. Among those praying for the health of Francis Thursday were a group of Mexican pilgrims, who paid a visit to the hospital.

"We would like to go in to kiss his feet," said another pilgrim, Flor Mercado Garcia, 66.

Garcia brought an offering of yellow flowers for Francis, but ended up placing it at the feet of the statue of John Paul II in front of the hospital, amid the growing mass of candles, drawings, and messages of support.

'Not there yet':

"For an 88-year-old who was already suffering from a chronic respiratory disease before the pneumonia, (his condition) remains critical at least until the improvement is defined as stable," they said in a joint interview with the Corriere della Sera daily.

Francesco Blasi, head of pneumology at Milan Polyclinic, and Stefania Vaglio, director of the Immune-haematology unit at the Sant'Andrea Polyclinic in Rome, said the pope's prognosis remains reserved because "the respiratory problem has not been resolved.

"We are not there yet. More days of waiting are needed". In the meantime, the "respiratory physiotherapy" Francis is doing is key for patients with severe pneumonia, Blasi and Vaglio said.

The exercises help them learn how to best use the muscles involved in breathing, they added. At 14 days so far, this current hospitalisation is Francis's longest. Despite his critical condition, Francis has kept up with Church matters from his hospital suite.

"The pope wants to push through decisions he cares about, it is a manifestation of strength, of a willingness to govern," Adriano Prosperi, a historian specialised in the Church, told the Repubblica daily.

Elected in 2013, Francis has aroused both fervour and fury within the Church with reforms aimed at opening the doors of a centuries-old institution to the modern-day faithful. "Francis knows that what he leaves behind is in danger, and wants to protect it", Prosperi said.