Pope Francis, 86, was admitted to a hospital in Rome on Wednesday with a respiratory infection which will require a stay of a few days, the Vatican said.
"In recent days Pope Francis has complained of some breathing difficulties," said Vatican spokesman Matteo Bruni in a statement.
The pontiff was admitted to Rome's Gemelli hospital for medical checks, which revealed "a respiratory infection... that will require a few days of appropriate hospital medical treatment", Bruni said, adding that a Covid-19 infection had been excluded.
Earlier in the afternoon, the Vatican had said Francis had been admitted "for some previously scheduled checks."
The pope, who this month marked 10 years as head of the Catholic Church, had earlier appeared in good spirits at his weekly audience at the Vatican, smiling as he greeted the faithful from his "popemobile".
However, he was seen grimacing as he was helped getting into the vehicle and Italian media reported he was taken to hospital by ambulance.
"Pope Francis is touched by the many messages received and expresses his gratitude for the closeness and prayer," said Bruni's statement.
A Vatican source said that the pope's appointments for Thursday morning were cancelled.
The Argentine pontiff suffers from chronic knee pain that has forced him to rely on a wheelchair in recent months.
The Gemelli was the same hospital where he underwent an operation on his colon in July 2021 after suffering from a type of diverticulitis, an inflammation of pockets that develop in the lining of the intestine.
He remained in hospital for 10 days. A year later he admitted he was still feeling the effects of six hours spent under anaesthetic during the surgery.
In an interview in January, Francis said the diverticulitis had returned.
Pope Francis had to cancel or curtail activities several times last year because of the pain in his knee and in a July 2022 interview acknowledged that he needed to slow down.
His health has been the frequent subject of speculation, particularly the question of whether he will follow the example set by his predecessor and retire if he cannot continue. (AFP)