Vatican City - Tens of thousands of people queued at St. Peter's Basilica in Vatican City on Monday to pay their last respects to the late pope emeritus Benedict XVI.

Shortly after 9:00 AM, the Vatican opened the doors of the basilica. People then moved forward along the central aisle and past the body.

The Vatican's police and security force, the gendarmerie, estimated that around 40,000 people had come to the cathedral by 2:00 PM.

Among the first mourners was Italian Prime Minister Giorgia Meloni. President Sergio Mattarella entered the basilica shortly before 9:00 AM, Agnello Stoia, the parish priest of St. Peter's Basilica, told the ANSA news agency.

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Benedict's long-time private secretary Georg Gänswein was also in the cathedral.

People had been lining up since the early hours of the morning, with a lengthy queue forming around St. Peter's Square.

"I want to say goodbye to him," said one person from Germany who had started queuing during the night.

The funeral service is set to take place in St. Peter's Square on Thursday at 9:30 AM, followed by the burial in the basilica.

Pope Francis himself is set to say the funeral Mass. One pope burying another is a historic event, made possible by Benedict's resignation in 2013.

According to official figures, up to 60,000 people are expected to attend the requiem, which Benedict had requested be kept simple.

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The former pontiff, whose birth name was Joseph Ratzinger, died on Saturday morning in the Vatican at the age of 95. It emerged on Wednesday that his health had deteriorated.

German-born Benedict XVI was the head of the Catholic Church from 2005 to 2013, when, after just under eight years as pope, he voluntarily resigned, becoming the first pope to do so in hundreds of years.

He cited his frailty, saying he lacked the strength for such a demanding job. His resignation may ultimately pave the way for future pontiffs to resign due to poor health.