According to the Vatican, Pope Francis will need to spend a few days in a Rome hospital due to a respiratory infection.
A statement stated that the 86-year-old did not have Covid, despite experiencing difficulties breathing in recent days.
It said he would require "a couple of long stretches of suitable clinic clinical treatment".
The statement went on to say that "Pope Francis is touched by the many messages received and expresses his gratitude for the closeness and prayer."
A person with direct knowledge told the BBC that his closest staff, including security, are likely to spend the night at the Gemelli Hospital.
This is the most active season for Pope Francis, with numerous occasions and administrations planned in front of Easter weekend.
This weekend is Palm Sunday Mass, and next week is Holy Week and Easter celebrations.
Additionally, a trip to Hungary is planned for the end of April.
On Wednesday morning, he directed his week after week broad crowd in St Peter's Square. He was seen grinning as he was helped into his vehicle, but he appeared to be in good spirits.
Italian media have questioned the Vatican's initial claim that the Pope had gone to the hospital for a previously scheduled check-up following the abrupt cancellation of a television interview.
President Joe Biden asked people to "make an extra prayer" for the Pope's recovery in response to the news.
The pontiff was also referred to as one of the "most Christ-like figures I've ever met" by Mr. Biden, who is only the second Roman Catholic to be elected as the leader of the United States.
Reuters received feelings from people in Buenos Aires, Argentina, the Pope's hometown. One man, Daniel Saco, said the pontiff "should find out if he can proceed".
Victoria Veira, who is originally from Brazil, stated, "It is very sad because, as a Latin American, I feel represented by this Pope, who is very open-minded and human."
Anibal Pizelle, who met the Pope when he was bishop of Buenos Aires, said that Francis was "physically and mentally strong" and a "person with enormous faith," so she was hopeful that he would recover.
In recent months, the Pope has used a wheelchair due to mobility issues with his knee.
He likewise went through a medical procedure to treat a colon issue in 2021. He stated that the condition had returned in January.
The pope has continued to be active and traveled abroad despite his ailments. In February, he went to the Democratic Republic of the Congo and South Sudan.