Pope Francis has called for prayers for the former head of the Catholic Church, Pope Emeritus Benedict XVI, the day after his death.

"Today we entrust the beloved pope emeritus Benedict XVI to the mother of God, to accompany him on his journey from this world to God," Pope Francis said on Sunday during the New Year's Mass in St Peter's Basilica.

"We all join together with one heart and soul in thanksgiving to God for the gift of this faithful servant of the Gospel and the Church," he said.

The former pontiff died on Saturday morning at the Mater Ecclesiae monastery in the Vatican Gardens, where he had lived since his resignation in 2013.

His last words were "Lord, I love you," his longtime secretary said on Sunday, quoting a nurse who helped care for the 95-year-old in his final hours.

Archbishop Georg Gaenswein, a German prelate who lived in the Vatican monastery where Benedict took up residence after his 2013 retirement, said the nurse recounted hearing Benedict utter those words at about 3am Saturday.

"Benedict XVI, with a faint voice but in a very distinct way, said in Italian, 'Lord, I love you,'" Gaenswein told the Vatican's official media, adding that it happened when the aides tending to Benedict were changing shifts.

"I wasn't there in that moment, but the nurse a little later recounted it," the archbishop said.

"They were his last comprehensible words, because afterwards, he wasn't able to express himself any more."

German theologian Joseph Ratzinger, as Benedict was born, will lie in state at St Peter's Basilica from Monday so the faithful can pay their respects.

The funeral is scheduled for January 5.

with AP

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