Pope Leo XIV visited the tomb of his predecessor Francis on Saturday to pray for the man he follows as the head of the Catholic Church, the Vatican said.

Vatican News published a photo of the white-robed American pope kneeling before Francis's simple marble tomb at Santa Maria Maggiore, the papal basilica in central Rome beloved of the Argentine pontiff, who died on April 21.

In a short statement, the Vatican's press office said Leo also prayed to the icon of the Virgin Mary at the basilica.

Long lines of the faithful are still queueing there to pay their respects to the former pope.

Shouts and clapping greeted his successor as he exited the basilica, video posted by Vatican News showed.

The visit capped a busy day for the 69-year-old Chicago-born pope.

He spent the morning addressing the College of Cardinals, telling them he would lead in the footsteps of Francis and calling himself an "unworthy successor" to St Peter.

From there, the former missionary paid a visit to a key Augustinian shrine southeast of Rome, where hundreds of faithful cheered his arrival.