The pope was admitted to hospital on February 14 with a severe respiratory infection. (Reuters: Guglielmo Mangiapane)
In short:
Pope Francis has had an episode of vomiting with aspiration and a sudden worsening of his double pneumonia.
The Vatican said the 88-year-old pontiff was alert and well-oriented and was continuing his treatments.
What's next?
The pope's doctors are expected to take 24-48 hours to evaluate how the episode will impact the state of his clinical condition.
Pope Francis has had an "isolated breathing crisis" in hospital, the Vatican said, in a setback as the 88-year-old pontiff battles double pneumonia.
The pope had "an episode of vomiting with aspiration and a sudden worsening of the respiratory condition."
"This afternoon … the Holy Father experienced an isolated bronchospasm crisis," the Vatican said, describing a constriction in the pope's respiratory airways — similar to an asthma attack.
He then received the help of "non-invasive mechanical ventilation."
The pope "has remained alert and well-oriented", the statement said, and is continuing his treatments.
Pope Francis is continuing treatment at Gemelli Hospital in Rome. (Reuters: Hannah McKay)
Today's update followed three days of more positive news, with the Vatican saying previously that the pope had been showing a "slight improvement" as he fights what has been termed a "complex" infection caused by two or more micro-organisms.
A Vatican official, who asked to remain anonymous, said the pope's breathing issue on Friday did not last a long time.
They said the ventilation the pope received involved the use of a light mask over his nose and mouth and his doctors are expected to take 24-48 hours to evaluate how the episode will impact the state of his clinical condition.
The pope has not been in critical condition for the past two days.
The pope has been in Rome's Gemelli hospital for two weeks, after being admitted on February 14 with a severe respiratory infection that triggered other complications.
Decorated candles, flowers and pictures of Pope Francis have been left outside Gemelli Hospital. (Reuters: Ciro De Luca)
Faithful gather
Catholics gathered at St Peter's Square in the Vatican on Friday, some holding rosaries, candles and religious pictures, as they prayed for Pope Francis.
"The whole world needs him because he's a man of peace and the world needs peace," Maria Rita, a faithful from Palermo, said. She described Francis as a grand pope and a 'revolutionary man'.
Rosemary Obiekosi, a visitor from Nigeria, shared her prayers for the Pope's recovery. "Apart from him being a pope, he's also human. So you don't wish someone to be ill," she said.
A prayer service was held in St Peter's Square. (Reuters: Alkis Konstantinidis)
The Vatican has not said how long the pope will remain in hospital, but it announced on Friday that Francis would not lead the annual Church service next week to open the Christian season of Lent.
The March 5 service, known as Ash Wednesday, starts the 40-day period leading up to Easter Sunday.
It will instead be entrusted to a senior Vatican official.
Francis, who has been pontiff since 2013 and is often described as working himself to exhaustion, has continued leading the Vatican from the hospital.
Catholics continue to gather in The Vatican while the pope remains in hospital. (Reuters: Alkis Konstantinidis)
On Friday, the Vatican released a papal letter to participants in a Church training course in Rome, which was signed by Francis with a note to say it was sent "from Gemelli hospital".
Francis has suffered several bouts of ill health over the past two years.
He is prone to lung infections because he developed pleurisy as a young adult and had part of one lung removed.
Double pneumonia is a serious infection of both lungs that can inflame and scar them, making it difficult to breathe.
Reuters