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

The 88-year-old pontiff went into the hospital 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.”

“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, a 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.

“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.

There were also prayers for the pope during Sunday services in Sydney and Melbourne.