Pope Francis has passed another "quiet night" in the Rome hospital where he has been battling pneumonia in both lungs for a month, the Vatican said on Friday.

Although he is no longer in critical condition, the 88-year-old pontiff still receives respiratory assistance through a nasal cannula during the day and an oxygen mask at night.

The Vatican said Francis had physiotherapy Thursday as well as his continuing treatment at the Gemelli Hospital.

He also tasted a cake to celebrate his 12 years of papacy, prayed and did his breathing exercises.

The Vatican press office said it would issue another medical bulletin Friday evening, but might stop sending a daily morning update. Talk is now turning to when he might go home.

But his hospital stay which began on February 14 -- the longest and most fraught of his papacy -- has raised doubts about his ability to lead the world's nearly 1.4 billion Catholics.

"It takes time for an 88-year-old body affected by bilateral pneumonia to recover, also in terms of energy, of strength," the press office said.