Pope Francis's ninth night in hospital passed peacefully after a respiratory attack that sparked alarm, the Vatican said Sunday, although the 88-year-old is still using oxygen through a tube to the nostrils.

The Vatican had on Saturday night warned that the condition of the pope, who is suffering from double pneumonia, was "critical" after he suffered a prolonged asthma-style attack and required blood transfusions for a low platelet count.

The Vatican's morning update was brief, saying only, "The night passed peacefully, the pope rested."

Yet Vatican sources pointed to this as evidence of no repeat of the crisis that occurred on Saturday at the Gemelli hospital, although he is still receiving oxygen through a cannula.

In a message published in lieu of his weekly Sunday Angelus prayer, which he normally delivers from a window overlooking St. Peter's Square, Francis thanked medical staff.

"I am confidently continuing my hospitalisation at the Gemelli Hospital, carrying on with the necessary treatment -- and rest is also part of the therapy!" he said in the message written in the past few days.

"I ask you to pray for me," he concluded in the message that was written in "recent days."

Suffering more

Francis, who has been head of the Catholic Church since 2013, was initially admitted to the Gemelli — which has a special suite for popes — on 14 February with bronchitis. 

In its evening update Saturday, the Vatican warned the pope had suffered a difficult day and his "condition continues to be critical, therefore... the pope is not out of danger."

It said Francis was alert and "spent the day in an armchair even if he was suffering more than" the day before.

It said the Jesuit had a "prolonged asthmatic respiratory crisis, which also required the application of high-flow oxygen."

Daily blood tests also "showed thrombocytopenia, associated with anaemia, which required the administration of blood transfusions," it added.

Thrombocytopenia is a condition that occurs when the platelet count in the blood is too low, which can cause trouble stopping bleeding — and can be life threatening.

Blood or platelet transfusions, delivered via an intravenous (IV) line, are given to people who are either bleeding heavily or at very high risk of bleeding, according to the US National Institutes of Health (NIH).

"The pope gets worse," headlined Italy's Corriere della Sera newspaper on Sunday, while La Repubblica described it as the "darkest day" at the Vatican.

Prayers for the Pope

As well as missing the Angelus prayers, Francis asked a senior prelate to take his place leading a morning mass Sunday as part of celebrations for the Jubilee 2025, a Catholic Holy year.

"Even though he is in a hospital bed we feel him close to us," Rino Fisichella said before reading out the homily at St Peter's Basilica, offering prayers for Francis in this "moment of trial."

Nuns and priests from around the world had sang and prayed for the pope on Saturday in front of Gemelli hospital.

Well-wishers have also been leaving candles bearing his picture at the foot of the statue on the site of former pope John Paul II.

"I am praying for him, for his health, because he is a special person for all of us," Italian teacher Ilde Zito told AFP on Sunday.

Michela di Geno, also offering prayers at the hospital, added: "We hope he recovers and long live the pope!"

Francis has said the papacy is a job for life, but has also left the door open to resigning like his predecessor.

Benedict XVI, a German theologian, in 2013 became the first pope since the Middle Ages to step down, citing his ailing physical and mental health.

Francis has repeatedly said it was not yet the time to quit — but his illness has raised fresh questions about his ability to stay on.

The pope maintains a punishing work schedule. He carried out a mammoth 12-day tour to the Asia-Pacific in September, but has suffered increasing health issues.

He underwent colon surgery in 2021 and an operation for a hernia two years later. He is overweight and has constant hip and knee pain, which forces him to use a wheelchair.