As a strong breeze blew, the pope's plain cypress coffin was carried out of St. Peter's Basilica by 12 pallbearers and placed before an altar set up outside the massive cathedral.
When the casket came into view, applause broke out among the hundreds of thousands gathered in giant Saint Peter's Square. Banners read "Santo Subito," or "Sainthood Immediately."
U.S. President George W. Bush, UN Secretary-General Kofi Annan, Iranian President Mohammad Khatami, Afghan President Hamid Karzai, Russian Prime Minister Mikhail Fradkov, Ukrainian President Viktor Yushchenko, and Azerbaijani President Ilham Aliev were among those in attendance.
The funeral was led by Cardinal Joseph Ratzinger, dean of the College of Cardinals, and a close confidant of John Paul.
In his homily, Ratzinger -- dressed in red vestments and a tall white miter -- hailed John Paul II as a "priest to the last." He said the pope had offered his life for God and the members of the church.
"Today, we bury the remains of Pope John Paul II in the Earth as a seed of immortality -- our hearts are full of sadness, yet at the same time of joyful hope and profound gratitude," Ratzinger said.
Ratzinger will have an influential voice in choosing Pope John Paul's successor and is considered a candidate himself.
He traced the pontiff's life from his days as a factory worker in Nazi-occupied Poland to his last moments as head of the Roman Catholic Church.
"Working in a chemical factory, surrounded and threatened by the Nazi terror, he heard the Lord's words: 'Follow me.' In this very particular context, he began to read books on philosophy and theology. Later, he joined the clandestine seminary," Ratzinger said.
The German-born Ratzinger choked with emotion as he recalled one of John Paul's last public appearances -- blessing the faithful from his studio window on Easter Sunday (27 March).
"For all of us, it remains unforgettable how on the last Easter Sunday of his life, the Holy Father, with suffering etched on his face, appeared at his window in the Apostolic Palace, and for the last time gave his 'Urbi et Orbi' blessing," said Ratzinger.
Around the world -- and especially in the pope's native Poland -- large crowds gathered to watch the funeral on television. An estimated 300,000 people assembled to pay their respects in Krakow, where he served as archbishop before becoming pope.
In Rome, more than 10,000 police, military, and paramilitary officers were deployed for the funeral. The airspace above central Rome was closed.
After the service, the bells of St. Peter's Basilica echoed across Rome as the pope's coffin was carried back inside.
The coffin was taken below to the church's crypt, where it was enclosed in a second zinc casket and finally in one made of oak.
The "camerlengo," or chamberlain, Cardinal Eduardo Martinez Somalo, performed the interment rite, concluding with the words: "Lord, grant him eternal rest, and may perpetual light shine upon him."
Vatican officials said the pope was buried in the crypt close to the spot said to contain the remains of Peter, the apostle chosen by Jesus Christ to found his church almost 2,000 years ago.
The pope died on 2 April at the age of 84 after struggling with several illnesses toward the end of his 26-year papacy.
Roman Catholic cardinals have decided to open a conclave to elect a new pope on 18 April.