Faithful wait for Pope Francis arrival for a mass in Kossuth Lajos Square in Budapest, Hungary, Sunday, April 30, 2023. AP
The 86-year-old Argentine pontiff is holding the mass at 9:30 am (0730 GMT) in Kossuth Lajos Square, behind the parliament located on the banks of the Danube.
Some 80,000 people were in attendance, according to the local authorities, under tight security.
"It is something quite unique to see the pope this close," university student Levente Kiss, 21, said.
"I feel emotional. He is very important in my life," onlooker Ferenc Toth, 43, told AFP after the pope passed by in his popemobile.
Francis will deliver his trip's last speech at 4:00 pm (1400 GMT) at a private Catholic university in Budapest to academics and those working in culture.
He will return to Rome in the early evening, giving his traditional press conference on the plane to journalists accompanying him on board.
On Saturday, Francis warned against "the evils of indifference" while greeting mostly Ukrainian refugees.
Prime Minister Viktor Orban's government -- in a departure from its usual anti-refugee position -- has welcomed those fleeing the war in Ukraine.
But activists say there is barely a support system in place. Orban's insistence on maintaining ties with Moscow has also alienated Ukrainians.
Francis' 41st international trip since becoming pope in 2013 is spent only in Budapest due to his fragile health, a month after being hospitalised for three days for bronchitis.
Despite persistent knee pain forcing him to move around in a wheelchair, the pope has appeared to be in shape while in the Hungarian capital.
Francis last visited the central European country -- where 39 percent of the 9.7-million population are Catholic -- briefly in 2021.
John Paul II was the first pope to visit Hungary, making trips in 1991 and 1996.