Pope John Paul II, the leader of the world's 1.1 billion Roman Catholics, died Saturday at the age of 84.

The Pope passed away at his apartment in the Vatican at 9:37 p.m. local time after suffering heart and kidney failure following two hospitalizations in as many months.

His body will lie in state for three days of public viewing, starting Monday, Vatican officials said.

A requiem mass was scheduled to begin in St. Peter's Square at 4:30 a.m. EDT Sunday, and a funeral date will be set next week, the Vatican announced. Italy has declared four days of national mourning.

"We all feel like orphans this evening," Undersecretary of State Archbishop Leonardo Sandri told the crowd of 70,000 people which had gathered in St. Peter's Square to pray for the pontiff.

The expected news initially silenced the crowd, but mourning soon turned to celebration as people began to clap and chant "Viva il Papa!" -- "Long live the Pope!"

Earlier Saturday, workmen were seen preparing the square for the upcoming papal events. A canopy used to shield the Pope from the sun was dismantled to make room for the millions of people expected to participate in the funeral.

Around Rome, efforts were already underway to find spaces large enough to accommodate the horde of people expected to make a special pilgrimage to the Eternal City.

Additional trains were being added across Italy to handle the extra passengers. In Poland, its national carrier said most of its Sunday and Monday flights to Rome were practically sold-out.

About two hours before the Pope died, the Vatican said he had developed a high fever, and was slipping in and out of consciousness. A day earlier, the Pope's heart and kidneys had begun to fail and his breathing was shallow.

The Pope suffered from Parkinson's disease and arthritis, and his health had deteriorated over the past few weeks.

In February, he was rushed to Rome's Gemelli hospital suffering from flu-related breathing problems.

He lost about 40 pounds after undergoing a tracheotomy, leading doctors to insert a feeding tube on March 30 to help him take nourishment.

The Vatican said he received the sacrament known as the Anointing of the Sick, commonly called Last Rites, on Thursday night.

John Paul visited Canada three times during his papacy, in 1984, 1987 and 2002.

Canada has three active cardinals who are eligible to vote to name John Paul II's successor.

They are Cardinal Marc Ouellet, who has been archbishop of Quebec since 2002; Cardinal Aloysius Matthew Ambrozic, who has been archbishop of Toronto since 1990; and Cardinal Jean-Claude Turcotte, who has been archbishop of Montreal since 1990.

About 44 per cent of Canadians consider themselves Roman Catholics, according to the latest census figures.