Pope Francis is no longer using mechanical ventilation for help breathing at night and his doctors believe he will continue to improve, the Vatican said on Wednesday, in the latest positive update as the 88-year-old pontiff battles pneumonia. 

Francis has been in Rome's Gemelli Hospital for nearly five weeks for a severe respiratory infection that has required evolving treatment.

The pope had been using non-invasive mechanical ventilation overnight during his hospital stay, which involves placing a mask over the face to help push air into the lungs.

Such ventilation had been "suspended", the statement said. But it said the pope is still receiving oxygen via a small hose under his nose.

The pope's doctors believe his infection is under control, the Vatican press office said shortly after the release of the latest statement. The pope does not have a fever and his blood tests are normal, it said.

The pope has been described as being in a stable or improving condition for two weeks, but the Vatican has not yet given a timeframe for his discharge, saying his recovery is going slowly.

Francis is prone to lung infections because he had pleurisy as a young adult and had part of one lung removed.

He has been receiving both respiratory physiotherapy to help with his breathing and physical therapy to help with his mobility. He has used a wheelchair in recent years due to knee and back pain.

Doctors not involved in Francis' care said the pope is likely to face a long, fraught road to recovery, given his age and other medical conditions.