Pope has been in hospital for more than two weeks.

Pope Francis was resting on Saturday morning following a quiet night, after suffering a health setback in his battle against double pneumonia, the Vatican said in its latest bulletin.

"The night passed peacefully, the Pope is resting", read the one-line statement from the Holy See press office.

The 88-year-old pontiff, who has spent the past two weeks in Rome's Gemelli hospital, on Friday afternoon suffered an "isolated" bronchial spasm which caused him to vomit and led to a "sudden worsening" of his respiratory condition, the Vatican said on Friday night.

The situation was complicated after the pope inhaled some of the vomit, the Vatican said, after which he was placed on “non-invasive mechanical ventilation” to help him to breathe.

The Vatican said it would take doctors 24 to 48 hours to assess how the bronchospasm would affect the pope's clinical condition, adding that Francis remained "alert and aware at all times" and that his prognosis is "guarded".

The setback came after health bulletins over the previous three days said there had been some "slight improvement" in the pope's medical condition, with test results showing that his mild kidney insufficiency had "subsided" while his lung inflammation was progessing "normally".

As Francis enters his 16th day in hospital, prayer vigils for his recovery continue outside the Gemelli and in St Peter's Square where a Rosary is being said each night.

Photo credit: Pavel Mikheyev / Shutterstock.com.