Pope Francis made his first public appearance since being discharged from hospital two weeks ago after treatment for double pneumonia, entering St Peter's Square at the Vatican in a wheelchair to greet cheering crowds.

Francis, 88, had been out of public view since 23 March, when he had given a short greeting before leaving Rome's Gemelli hospital after more than five weeks of treatment in the most serious health crisis of his 12-year papacy.

The Pope came out to the square shortly before noon at the end of the celebration of a mass for the church's Jubilee year.

Arriving in front of the main altar for the service in bright sunshine, Francis waved to the crowds, before speaking briefly.

"Happy Sunday to everyone," the Pope said, speaking in a frail voice while receiving oxygen via a nasal cannula. "Thank you so much."

The Pope smiled broadly as he greeted crowds. His voice, though weak, sounded stronger than it had during the 23 March appearance, when he struggled to speak.

Francis usually offers a weekly noon-time prayer in St Peter's Square on Sundays. But he has not been able to do this since 9 February, before going to hospital.

He was admitted to hospital on 14 February for a bout of bronchitis that developed into double pneumonia, an especially serious condition for him as he had pleurisy as a young adult and had part of one lung removed.

Francis came so close to death at one point during his 38-day stay in hospital that his doctors considered ending treatment so he could die in peace, the head of his medical team said last month.

This morning's mass was part of a special celebration in honour of healthcare workers and those who are sick. In a written message released by the Vatican shortly after noon, Francis said he had felt God's closeness during his time in hospital.

"I ask the Lord that this touch of his love might reach all those who suffer and encourage those who are taking care of them," said the text.

It is unclear how often the Pope will appear in public in the coming weeks, with Easter Sunday just two weeks away.

Doctors have prescribed Francis with a two-month period of rest at his Vatican residence, to allow his ageing body to heal, and the Vatican has removed all previous commitments from the pope's calendar.

Britain's King Charles, who is coming to Italy next week for a state visit, has cancelled a planned meeting with Pope Francis.

The Vatican has not said yet whether the Pope will be able to lead the celebrations on 20 April for Easter.