Pope Francis resting, stable as nears three weeks in hospital

For the last three nights Francis -- who had part of a lung removed as a young man -- has worn an oxygen mask to help him sleep.

On Thursday morning, as the previous day, he switched to a less onerous nasal cannula -- a plastic tube tucking into his nostrils -- which provides high-flow oxygen, a Vatican source said.

Francis missed the formal Ash Wednesday celebrations in Rome marking the start of Lent, but took part in a blessing in his private suite on the 10th floor of the Gemelli.

The Vatican has been providing twice daily updates on the pope's health.

But the leader of the world's almost 1.4 billion Catholics has not been seen in public since his hospitalisation -- the longest of his papacy.

Nor has the Vatican issued any photos, although Francis has published several texts.

- 'Thoughts and prayers' -

During previous hospitalisations, the pope appeared on the Gemelli balcony for his weekly Angelus prayer at noon on Sundays.

But he has missed the last three, and no announcement has yet been made about whether he will make an appearance this weekend.

The Vatican confirmed Thursday that senior cardinal Michael Czerny would stand in for the pope and lead the mass this weekend marking the first Sunday of Lent.

The mass was also part of celebrations for the Jubilee 2025, a Holy Year led by the pope, dedicated this weekend to volunteers.

The Holy See said Thursday the event "takes on an even deeper meaning, as the thoughts and prayers of all the brothers and sisters turn to the Holy Father and the experience he is going through".

Pilgrims will pray in front of the hospital on Saturday, it said, as well-wishers have since Francis was admitted.

The pope was initially diagnosed with bronchitis but this developed into pneumonia in both lungs, sparking alarm across the globe.

On February 22, he suffered a "prolonged asthmatic respiratory crisis" and on February 28 had "an isolated crisis of bronchospasm" -- a tightening of the muscles that line the airways in the lungs.

On Monday, Francis "experienced two episodes of acute respiratory failure, caused by a significant accumulation of endobronchial mucus and consequent bronchospasm", according to the Vatican.

Francis's health has regularly led to speculation, particularly among his critics, as to whether he could resign like his predecessor, Benedict XVI.