VATICAN CITY — Pope Francis made a surprise entrance to St. Peter’s Square during a special Jubilee Mass for the sick and health workers on Sunday, marking his first public appearance at the Vatican since leaving t he hospital two weeks ago after a life-threatening bout with pneumonia.

The pontiff waved at the crowd of faithful that stood and applauded as he was pushed in a wheelchair unannounced to the front of the altar in the square. Some exclaimed, “I see the pope!’’ as his image first emerged on a big screen showing him passing through the Holy Door before being brought down a ramp to the altar.

“Good Sunday to everyone,’’ Francis said, speaking into a microphone, which he tapped to make sure it was working on a second attempt. “Thank you very much.”

The pontiff’s voice sounded stronger than when he addressed well-wishers outside of Gemelli hospital on the day of his release March 23, after a five-week hospital stay. He wore nasal tubes to receive supplemental oxygen, which the Vatican says is being gradually reduced.

— The Associated Press