Pope Francis paid homage Saturday to "noble" and "kind" ex-pope Benedict XVI, who has died at the age of 95, a decade after becoming the first pontiff since the Middle Ages to resign.

"With emotion we remember a person so noble, so kind," Francis said in a moving tribute to his predecessor at a New Year's Eve service in St Peter's Basilica.

He thanked the conservative German theologian, born Joseph Ratzinger, "for all the good he has done", and underlined "his sacrifices offered for the good of the church".

Benedict died at 9:34am (0834 GMT) in the Mater Ecclesiae Monastery in the Vatican, where he had lived since he resigned.

He had shocked the world in 2013 when he became the first pope in nearly six hundred years to step down, citing his declining mental and physical health.

In his spiritual testament, written in August 2006 and published Saturday evening, he wrote: "I ask for forgiveness from the bottom of my heart from all those whom I have wronged in some way."

His death brings to an end an unprecedented situation during which two "men in white" -- Benedict and Francis -- co-existed within the walls of the tiny city state.

Benedict's body will be displayed from Monday morning in St Peter's Basilica to allow the faithful to pay their respects, ahead of a "solemn but simple" funeral, the Vatican said.

He will be buried in the papal tombs under St Peter's Basilica.

- 'Outstanding theologian' -

Tributes poured in for a man described by Archbishop of Canterbury Justin Welby as "one of the greatest theologians of his age", a message echoed by the head of the Russian Orthodox Church, Patriarch Kirill.

Ukraine's President Volodymyr Zelensky hailed the late pope as an "outstanding theologian, intellectual and promoter of universal values", after Russian President Vladimir Putin called Benedict a "defender of traditional Christian values".

US President Joe Biden, the second Catholic to hold the presidency, said the late pope "will be remembered as a renowned theologian, with a lifetime of devotion to the Church, guided by his principles and faith".

Britain's King Charles praised his efforts to "promote peace" between Catholic and Protestant communities, while UN chief Antonio Guterres praised Benedict's "tenacious commitment to non-violence and peace".

But Benedict's staunch defence of traditional Catholic teaching on abortion, euthanasia and gay marriage alienated many Catholics. His eight-year papacy was also marred by in-fighting at the Vatican and the scandal of clerical child sex abuse.

- A great pope -

Benedict's death was met with sadness among many holiday visitors Saturday to St Peter's Square.

"We are distraught," said Davide Di Tommaso, 30, from the southern Italian region of Molise. "He was truly a great pope."

Benedict's health had been declining for a long time, and he had almost entirely withdrawn from public view when the Vatican revealed on Wednesday that his situation had worsened.

That same day, Francis called for Catholics worldwide to pray for him and he received the last rites, a Catholic tradition for the dying.

Benedict is the first pope to die since the long-reigning and popular John Paul II, whose funeral mass in 2005 in St Peter's Square drew an estimated one million people, including heads of state.

- In-fighting and scandal -

Born on April 16, 1927 in Marktl am Inn, in Bavaria, Benedict was 78 when he became the first German pope of the modern era.

Flags on the town hall flew at half-mast Saturday in Marktl, where a special mass was organised at the church where he was baptised.

Local Karl Michael Nuck, 55, said his death "was probably a deliverance", while praising Benedict for resigning and defending his record.

Long close to John Paul II and a senior cardinal in the Catholic hierarchy, Benedict was a leading candidate to become pope in 2005 -- but later said his election felt "like the guillotine".

Unlike his successor Francis, a Jesuit who delights in being among his flock, Benedict was a conservative intellectual dubbed "God's Rottweiler" in a previous post as chief doctrinal enforcer.

He struggled to contain numerous scandals in the church during his papacy, not least the worldwide scourge of clerical sex abuse and decades of cover-ups.

The abuse scandal overshadowed his final months after a damning report for the German church in January 2022 accused him of having failed to stop four predatory priests in the 1980s while archbishop of Munich.

He denied wrongdoing and the Vatican strongly defended his record in being the first pope to apologise for the scandals, who expressed his own "deep remorse" and met with victims.

- Conservative standard-bearer -

There were other controversies, from comments that angered the Muslim world to a money-laundering scandal at the Vatican bank and a personal humiliation when, in 2012, his butler leaked secret papers to the media.

He will be remembered for his theology, but "he didn't have the mental strength to be pope", noted Italian Vatican observer Marco Politi.

Yet after he quit, Benedict remained a flag-bearer for the conservative wing of the church.

In an interview in March 2021, he said "there is only one pope", but acknowledged "fanatical" supporters who refused to accept his resignation.

With his death, those who battled Francis' more liberal outlook "lose a living symbol", Politi told AFP.