Looking tired and drawn, Pope Benedict XVI has thanked the public for their "love and prayers" in his first public appearance since announcing his shock resignation.

The Pope was cheered by crowds as he entered and began speaking, at a weekly audience in a hall at the Vatican. Thousands of people gathered in the hall to greet him, giving him a standing ovation as he arrived, and cheering as he began and finished speaking.

He repeated his rationale behind his decision to step down, saying he did it "for the good of the Church", aware of his own declining spiritual and physical strength.

Pope Benedict thanked the public for their warm greeting and their sympathy.

"Thank you for the love and prayer with which you have accompanied me... Keep praying for me, for the Church and for the future pope," he said.

He said he was aware of the gravity of his decision to resign but also of his declining strength, adding that he was certain the Church would sustain him with prayer.

"I did this in full liberty for the good of the Church," he added.

The 85-year-old will continue with his diary as usual until the day he officially retires at the end of February, Vatican officials say.

By the end of Lent, in six weeks' time, there is expected to be a new Pope.

Meanwhile it emerged that the afternoon Mass has been relocated. The pontiff had been scheduled to celebrate Ash Wednesday at the small Sant' Anselmo church, then lead a procession to Santa Sabina Basilica on Rome's Aventine Hill.

The Vatican said the change to St Peter's was to accommodate the crowds, but it will also save the Pope the effort of the procession.