Pope Francis delighted worshippers on Palm Sunday with an impromptu tour of St. Peter's Square, against the advice of his doctors to avoid crowds while recovering from pneumonia.

For the second Sunday in a row after the longest hospital stay of his papacy, the 88-year-old pontiff left his Vatican quarters, handing out sweets to children and shaking hands while doing the rounds of the Vatican landmark.

While sat in his wheelchair, the Argentine appeared in rather good form, without the nasal cannula — a plastic tube tucked into the nostrils — used to help him breathe during his convalescence.

Since his release from hospital, the Pope has ventured out on several occasions despite his doctors urging him to rest, with his surprise visits appearing on no official Vatican programme.

On Thursday, he made an unscheduled visit to Saint Peter's Basilica to inspect renovation work and to visit the tomb of Pius X, before making a trip on Saturday to pray at his favourite basilica, Santa Maria Maggiore in Rome.

And after his planned meeting with King Charles III was initially cancelled due to his ill health, Francis welcomed the British monarch and Charles's second wife Queen Camilla in private on Wednesday.

The extent of his participation in next week's Easter celebrations — the holiest period of the Christian calendar — is however yet to be confirmed by the Holy See.

In his Sunday Angelus prayer, released by the Vatican, the pontiff thanked the flock for their prayers and issued his customary call for peace in the world.