Thousands gathered in St. Peter's Square on Sunday to attend a Mass honoring Pope John Paul II (search), the leader of the Roman Catholic Church who died Saturday at the age of 84.
The traditional Sunday noontime prayer, which John Paul had delivered throughout his 26-year pontificate, would follow, the Vatican said.
The throngs that filled the square Sunday joined some of the faithful who had held an overnight vigil in the piazza after learning of the death of the pontiff.
On Saturday, the pope's death was announced in a statement from the Vatican which stated that "The Holy Father died this evening at 9:37 p.m. [2:37 p.m. EST] in his private apartment. All the procedures outlined in the apostolic Constitution 'Universi Dominici Gregis' (search) that was written by John Paul II on Feb. 22, 1996, have been put in motion."
The announcement came from papal spokesman Joaquin Navarro-Valls (search) and was distributed to journalists via e-mail.
John Paul expired as cardinals were leading some 70,000 people at St. Peter's Square in prayers for the pope in his "last journey."
Bells tolled at the Vatican and across Rome, and Vatican, Italian and European Union flags were being lowered to half-staff across the capital.
In the United States, President Bush ordered flags lowered at the White House and all federal buildings and military facilities until the pope is buried.
And in what may be the most profound testament to John Paul II's capacity to reach across borders, the news of his death sent Catholics, Protestants, Jews and Muslims to their respective houses of worship to pray for him.
A Mass was scheduled for St. Peter's Square at 10:30 a.m. (4:30 a.m. EDT) Sunday. The pope's body would be taken to the basilican no earlier than Monday afternoon, the Vatican said.
The College of Cardinals (search), the red-robed "princes" of the Roman Catholic Church, were heading toward the Vatican to prepare for the secret duty of locking themselves in the Sistine Chapel (search). They were meeting at 10 a.m. (4 a.m. EDT) Monday in a pre-conclave session, and were expected to set a funeral date between Wednesday and Friday.
The pope died after suffering heart and kidney failure following two hospitalizations in as many months. Just a few hours earlier, the Vatican said he was in "very serious" condition but was responding to members of the papal household.
John Paul II was last seen in public on Wednesday when, looking gaunt and unable to speak, he appeared briefly at his window.
His health sharply deteriorated the next day when he suffered a high fever due to a urinary tract infection. The Vatican said the pope was suffering from septic shock, which involves bacteria entering the bloodstream and a consequent over-relaxing of the blood vessels.
As the end drew near, the pontiff refused to be taken to a hospital and chose to spend his final hours in the papal apartment in Rome.
Though he had difficulty speaking following surgery on his throat last month to help him breathe, the pope was communicative until the end, aides said.
Navarro-Valls said that upon being informed of the masses of young people holding vigil outside his window, the pope, who had worked so tirelessly advocating for the world's young, said: "I have looked for you. Now you have come to me. And I thank you."
According to news channel Sky Italia, the pope's private secretary, Archbishop Stanislaw Dziwisz (search), held his hand as he died.
John Paul reportedly looked out the window and uttered his last word: "Amen."
'The Pilgrim Pope'
Millions all over the world had awaited word of what seemed inevitable, as the Vatican began preparing the pope's flock for his death.
Since Thursday, when the Vatican announced John Paul was gravely ill, hundreds of thousands of people have stood in St. Peter's Square, holding candles, singing and praying for a man beloved by so many.
But knowing the pope was fading did little to stem the tide of grief after he died.
Immediately after the news was announced to the crowd in St. Peter's Square, there was complete silence. The crowd seemed stunned.
A few minutes later, some people broke out in applause in appreciation for the pope — an Italian tradition in which mourners often clap for important figures. Others wept.
"We all feel like orphans this evening," Undersecretary of State Archbishop Leonardo Sandri (search) told the crowd gathered below the pope's still-lighted apartment windows.
Cardinal Angelo Sodano (search), the Vatican's No. 2 official, immediately led the tearful throng in prayers. Some people held their hands to their heads in disbelief; on other faces, tears rolled uncontrollably.
After the crowd started recovering from stunned silence, a group of youths sang, "Hallelujah, he will rise again," while one of them strummed a guitar. Later, pilgrims joined in singing the "Ave Maria."
"He was a marvelous man. Now he's no longer suffering," said a tearful Concetta Sposato, a pilgrim who heard the pope had died as she was on her way to St. Peter's to pray.
"My father died last year. For me, it feels the same," said Elisabetta Pomacalca, a 25-year-old Peruvian who lives in Rome.
"I'm Polish. For us, he was a father," said pilgrim Beata Sowa.
As the most traveled pontiff in history, John Paul often referred to himself as "the pilgrim pope." Millions attended the masses he led in cities all over the world, and visits to the Middle East and impoverished African nations won him admirers from people of other faiths and even no faith at all.
In the United States, the president led Americans in mourning the pope.
"The world has lost a champion of human freedom" Bush said Saturday afternoon at the White House. "A good and faithful servant of God has been called home."
The president and first lady Laura Bush later attended a memorial Mass at St. Matthew's Cathedral in Washington. Bush was expected to attend the pontiff's funeral, but the White House held off making an official announcement of the delegation it would send out of respect for protocol.
Christians, Jews and Muslims in the fractious Middle East put their differences aside to express gratitude for the Holy Father's efforts to bring them together.
"This is a sad day, we are very sad to lose him," said a spokesman for the Arab League. "We will never forget his noble stance in support of the oppressed people, including the Palestinians."
Palestinian leader Mahmoud Abbas said the pope "devoted his life to defending the values of peace, freedom and equality."
American Muslims also marked the pontiff's passing.
"We offer our sincere condolences to members of the Roman Catholic Church and to all those who seek a more peaceful world," said the Washington-based Council on American-Islamic Relations in a statement.
People in Pope John Paul II's hometown of Wadowice wept as the news of his death reached them at the end of a special Mass in the church where Poland's favorite son worshipped as a boy.
The Rev. Jakub Gil came to the front of the church as the last hymn died away.
"His life has come to an end. Our great countryman has died," he said.
People both inside and outside the church fell to their knees.
In Warsaw, church bells rang and traffic halted. At Pilsudski Square, the former Victory Square where he conducted a mass in 1979 in then-communist Poland, people laid flowers in the form of a cross. Others walked to church holding candles.
Church Prepares for New Leader
When a pope dies, the prefect of the papal household, currently American Archbishop James Harvey, informs the camerlengo, or chamberlain, who will be the most important official running the Holy See in the period between the death of a pope and the election of a new one.
The camerlengo, now Cardinal Eduardo Martinez Somalo (search) of Spain, must then verify the death — a process which in the past was done by striking the forehead of the pope with a silver hammer.
The camerlengo then calls out to the pope three times by his baptismal name — Karol, Karol, Karol. When the pope does not respond, the camerlengo then announces, "The pope is dead."
The camerlengo then uses the silver hammer to smash the pope's ring — the papal seal or "ring of the fisherman" — to preclude forgery of official documents.
An official nine-day mourning period, known as the "novemdiales," follows the death of a pope. The pope's body lies in state in St. Peter's Basilica (search) in the Clementine Chapel.
The Vatican announced early Sunday that John Paul II's body would be brought to the basilica no earlier than Monday afternoon.
The funeral and burial must be held between the fourth and sixth day after death. Weather permitting, it would be held in St. Peter's Square. Most popes in recent centuries have chosen to be buried beneath St. Peter's Basilica.
Even as John Paul's death neared, members of the College of Cardinals were already headed toward the Vatican. The conclave of 117 cardinals are tasked with electing a new pope.
Among possible successors are German Cardinal Joseph Ratzinger (search) — one of the pope's closest aides and the Vatican's doctrinal watchdog.
Others mentioned include Brazilian Cardinal Claudio Hummes, Cardinal Oscar Andres Rodriguez Maradiaga of Honduras, Cardinal Francis Arinze, a Vatican-based Nigerian, Cardinal Christoph Schoenborn of Austria and Cardinal Dionigi Tettamanzi of Italy.
FOXNews.com's Marie-France Han, Jane Roh and The Associated Press contributed to this report.