Roman Catholics worldwide prayed on Sunday for Pope Francis, who is hospitalized in critical condition, after the Vatican announced that he was “not out of danger.”

Francis, 88, was admitted to a hospital in Rome on Feb. 14 with an infection that developed into pneumonia in both lungs. He had a long “asthmatic respiratory crisis” on Saturday that required “high flows of oxygen” and a blood transfusion, the Vatican said.

Francis has been the spiritual leader of almost 1.4 billion Roman Catholics around the world since 2013. And around the world, there have been prayers for his recovery.

At the Myeongdong Cathedral in Seoul, Pat Santos, a tourist from the Philippines, described the pope as “the symbol of Christianity.”

The Vatican said on Sunday morning that the pope had had a restful night, without providing further details about his condition.

“Pneumonia is a serious illness for his age, that’s why we should be worried,” said Mr. Santos, 31, who was visiting South Korea with his family. “May he recover very well so that he can enjoy his retirement.”

Francis has suffered damage to his lungs in the past, and in recent days, a few cardinals have openly spoken about the possibility of him resigning, as his predecessor, Benedict XVI, did in 2013.

Doctors had said on Friday that Francis would remain in the Policlinico Agostino Gemelli hospital in Rome for at least another week. They had said he was in critical condition on Friday, too, but the announcement on Saturday indicated a more complicated situation.

There were prayers for the pope during Sunday services in Nairobi, Kenya, as well as in Sydney and Melbourne in Australia; in the Philippines, where almost 80 percent of the population is Roman Catholic; and in East Timor, which the pope visited last year and where nearly everyone is Catholic.

“Once more, we continue to keep in our prayers Pope Francis. May the Lord continue to extend to him his love, his mercy and his healing,” Father Vicente Gabriel Bautista said during Sunday Mass at the Manila Cathedral, which also held a special prayer vigil for Francis on Friday.

Aurora Agustin, a candle vendor, said she had been sitting outside the Quiapo Church in Manila and praying since Friday.

“I pray for his speedy recovery because he is our leader and is very well loved,” said Ms. Agustin, 54.

Neneth Felix, a church volunteer in Paranaque, south of Manila, said she was praying for Francis to have a longer life.

“When I pray for my family at night, I include Pope Francis in my prayers,” said Ms. Felix, 62. “I am touched by his humility — everything about him reflects it.”

Catarina Baros, 16, in Dili, East Timor, said that she had just come from Mass and had lit a candle before a statue of St. Anthony.

“I did not want Papa Francisco to be sick, because he came to visit Timor. As a young girl I was very happy with his presence in Timor last year, because he gave blessings.”

Aie Balagtas See contributed reporting from Manila, and Zevonia Vieira from Dili, East Timor.