Pope Benedict XVI bestowed the status of "blessed" on the late John Paul II this morning in Saint Peter's Square, filled to overflowing as more than one million people took part in the solemn mass.
The throngs cheered as Pope Benedict pronounced the formula of beatification for John Paul and a giant banner bearing the Polish pontiff's portrait was unveiled over the facade of St Peter's basilica.
Pilgrims waved flags from around the world in the sun-drenched square, reprising the chant of "santo subito" (sainthood now) that they had shouted at John Paul's funeral six years ago.
Experts say the beatification could help the Vatican burnish an image badly tarnished by paedophile priest scandals, but others have been critical of the fast-tracking of a process that usually takes decades.
Pope John Paul's pontificate lasting nearly 27 years helped inspire youth groups and lay religious movements, but his critics accused him of turning a blind eye to the child abuse scandals which first erupted in the United States in 2000.
Many people agree however that it was a remarkable papacy during which Pope John Paul survived an assassination attempt in 1981, built ties with Judaism and Islam and even apologised for the mistakes and sins of the Catholic Church.
Pope John Paul was elected Pope in 1978, becoming the first non-Italian pontiff in more than four centuries. He became known for his extensive foreign travel and succeeded in giving new strength to the Church before illness sapped his energies.
He died on April 2, 2005, in agony from an acute case of Parkinson's.
Among the attendees at the mass was Zimbabwean President Robert Mugabe, who arrived in Rome yesterday under a special exemption from a European Union travel ban imposed in 2002 over extensive human rights abuses in his country.
Italy's opposition has also been sceptical over the praise for Pope John Paul from twice-divorced Prime Minister Silvio Berlusconi, who will be attending despite the Vatican's often pointed criticism of his wild sex life.
Following the mass, Pope Benedict will pay his respects in front of Blessed John Paul's coffin, which was exhumed on Friday and placed inside Saint Peter's basilica.
Pilgrims will then file past the simple wooden coffin, which will be laid to rest again tomorrow in a chapel near Michelangelo's famous Pieta statue.
Thousands of pilgrims have swarmed into Rome in recent days ahead of the ceremony -- many travelling on specially chartered buses, ferries and planes.
In a message to the world's 1.1 billion Catholics ahead of today's grand ceremony, Pope Benedict called the weekend of prayer "a feast of faith".
The Vatican's official daily said it was "an extraordinary event without precedent in the last 1,000 years of the Church's history."
The beatification became possible after the Vatican confirmed a miracle attributed to Pope John Paul's intercession -- the unexplained healing of a French nun, Marie Simon-Pierre, from Parkinson's disease.
Simon-Pierre spoke at yesterday's vigil, paying tribute to Pope John Paul as "a shepherd ... who was closest to the weak, the sick and the young."
The Vatican needs to certify a second miracle before Pope John Paul can be made a saint, but officials have hinted that this could happen soon.
Pope Benedict also paid tribute to his "great predecessor" in a short televised message to the people of Pope John Paul's native Poland.
"I share with you the joy that fills my heart and my spirit," he said.
Thousands of pilgrims have arrived from Poland, and some of them waved flags from the historic trade union movement Solidarity, which the late pope supported in its struggle against communist power in the 1980s.
"I feel very excited. It's a great opportunity to share this historic moment. We didn't sleep all night but I'm more excited than tired," said Belen Lavilla, 12, who came by boat from Barcelona with hundreds of young people.
A Polish woman in a cream-coloured national dress with red flowers, 48-year-old Margerit Solik said: "It's a great day full of emotion!"
Stanislaw Motyka, 62, who also wore a traditional Polish costume, said the vigil before Pope John Paul's beatification had been "absolutely magical".
"My only hope is to live to see him be made a saint," he said.