Pope Francis praised Pope Emeritus Benedict XVI's "acute and gentle thought" during a general audience in the Vatican, as tens of thousands of admirers of the retired pontiff filed by his body lying in state in Peter's Basilica on the final day of viewing.

By the time the basilica's doors were shut to the public on Wednesday evening, some 200,000 people had paid their respects over three days of viewing.

After the closure, Vatican officials were preparing to place the 95-year-old German churchman's body into a wooden coffin, ahead of Thursday morning's funeral in St Peter's Square.

Among the last viewers were a married couple from Calabria. Gaspare Guadagnuolo, 73, and Lina Proto, 62, said they remember a visit by Benedict to that southern region years ago.

"I was struck by people's participation," Proto said. "There was a lot of intense emotion."

At his customary weekly audience, Francis was greeted by an enthusiastic crowd in Paul VI auditorium and shouts of "Viva il papa!" or "Long live the pope."

"It is my duty to come," said Małgorzata Nowska, a Polish resident of Rome as she paid tribute Wednesday. She said she wanted to give Benedict "a last hug, a last prayer."

Francis is due to preside over Benedict's funeral, an event drawing heads of state and royalty despite Benedict's requests for simplicity and Vatican efforts to keep the first funeral for an emeritus pope in modern times low-key.

Only Italy and Germany were invited to send official delegations, and German President Frank-Walter Steinmeier and Italian President Sergio Mattarella confirmed their participation.

But other heads of state and government decided to take the Vatican up on its offer and come in their "private capacity." They included several other heads of state, at least four prime ministers and two delegations of royal representatives. All were attending in what the Vatican describes as a "private" role.

And in a further sign of officialdom, the Italian government announced it was lowering all Italian and European Union flags to half-staff on public buildings across the country Thursday.

Francis drew applause when he opened his remarks by giving a shout-out to all those who were outside paying tribute to Benedict, whom he called a "great master of catechesis."

"His acute and gentle thought was not self-referential, but ecclesial, because he always wanted to accompany us in the encounter with Jesus," Francis said.

― With AAP.