Cardinals will meet this morning for the first time since Pope Francis died to confirm the details of his funeral.
The world will be watching Vatican City after the death of the 88-year-old pontiff on Easter Monday.
Francis died after a cerebral stroke that led to a coma and irreversible heart failure, the Vatican said.
Tributes poured in from around the world yesterday, including from President Michael D Higgins and other world leaders, with many praising the Pope for his advocacy for the marginalised.
President Higgins said there was a "warmth" to the Pope, and that he brought a "unique humility" to the role.
UK Prime Minister Keir Starmer said Francis had been "a Pope for the poor, the downtrodden and the forgotten".
His death starts a centuries-old ritual, where first the camerlengo, Irish-born Cardinal Kevin Farrell, certifies Pope Francis's death and seals the papal apartment.
Cardinal Farrell will carry out the administrative and financial duties of the Holy See until a new pope takes over.
Before the cardinals, senior members of the Catholic Church, convene in the Sistine Chapel for the conclave - the secret meeting at which a new pope will be elected - the Church enters a period called "sede vacante", or "the vacant See".
The Pope's body will remain in the chapel for a few days before being brought for public viewing in St Peter's Basilica, as per new rites Francis approved last year.
The public will likely be able to begin paying their final respects to Francis starting on Wednesday, the Vatican said.
The funeral date has not yet been confirmed, but it must be held between four and six days after the death and is set to be announced after the cardinals meet this morning.
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US President Donald Trump said on social media he and his wife Melania plan to attend the funeral.
After the funeral, there are nine days of official mourning, known as the "novendiali".
To give everyone time to assemble, the conclave must begin 15 to 20 days after the sede vacante is declared, but it can start sooner if the cardinals agree.
Cardinals, including the Archbishop of Westminster Cardinal Vincent Nichols, and Cardinal Timothy Radcliffe, from London, will take part in the vote for the next pope.
Both aged 79, the pair are just below the cut-off for voting as part of the conclave.
Only cardinals under the age of 80 are eligible to vote in a conclave - they are known as the cardinal electors and their number is limited to 120.
Asked about the next pope at a press conference yesterday, Cardinal Nichols told reporters: "He has to be a man of great inner strength, and I think great inner peace."
He added: "I think those inner capacities of closeness to God and peace are the absolute essentials."
Cardinal Radcliffe said: "I think that we always open ourselves to be surprised. All recent popes have been quite different from each other."
