Pope Francis has sent his first audio message since being hospitalised for double pneumonia nearly three weeks ago, expressing thanks “from the bottom of my heart” to well-wishers around the world who have offered their support.

A brief, two-line message recorded by Francis from Rome’s Gemelli hospital earlier on Thursday (local time) was played during a nightly prayer service for the Pope in St Peter’s Square at the Vatican.

“I thank you from the bottom of my heart for your prayers in the Square for my health,” said the pope, speaking in his native Spanish, and pausing every few words to take a deep breath.

“May God bless you.”

The audio message came shortly after the Vatican said the pontiff had remained stable on Thursday and had no new episodes of respiratory crisis.

In a sign of progress as the 88-year-old pontiff continues treatment, the Pope’s doctors said they would not issue another medical bulletin until Saturday, “considering the stability of the clinical picture”.

Francis was admitted to Gemelli hospital on February 14 with a severe respiratory infection that has required continuously evolving treatment.

In the latest detailed medical update on his condition, the Vatican said the Pope had no fever and his blood tests remained stable.

Despite pausing the daily readouts about his condition, the doctors continued to call the Pope’s prognosis “guarded”, meaning he was not yet out of danger.

The tone of the updates from the Vatican has been more upbeat in recent days, following what was described as two episodes of “acute respiratory insufficiency” on Monday.

On Thursday, the Vatican said the Pope had been able to work between receiving his treatments and taking rest.

It also said the pontiff, who has used a wheelchair in recent years due to knee and back pain, had continued with some physical therapy to help with mobility, which first started on Wednesday.

Monday’s respiratory episodes had required Francis to use non-invasive mechanical ventilation, which involves placing a mask over the face to help push air into the lungs.

The Pope is now only receiving ventilation at night, said the Vatican. During the day, he receives oxygen via a small hose under his nose.

Francis has not been seen in public since entering hospital, his longest such absence since his papacy started 12 years ago. His doctors have not said how long the treatment might last.

The Pope, who is known to work himself to exhaustion, has continued to work from hospital. On Thursday, the Vatican announced the appointments of two bishops that would have required his approval.

The Pope has had several bouts of ill health in the past two years. He is prone to lung infections because he had pleurisy as a young adult and had part of one lung removed.

Double pneumonia is a serious infection in both lungs that can inflame and scar them, making it difficult to breathe.

-AAP