Hundreds of thousands of people from around the world converged on St. Peter's Square on Sunday to attend the sainthood ceremony of Pope John XXIII and John Paul II, two giants of the Catholic Church in the 20th century.

Some, including many families, waited for more than 12 hours along the main street leading to the Vatican before police opened up the square at 5:30 a.m. local time, about four hours before the ceremony was due to start.

"Open up! Open Up! Let us in!" the sometimes nervous crowd chanted, with many expressing exasperation with the wait.

"We have been in this spot since 5 p.m. yesterday," said Maria Huszaluk, 19, one of a Polish family of six who came from Belgium to see Pope Francis make their most famous native son a saint.

One of her two smaller sisters slept in her arms.

Via della Conciliazione, the half kilometre-long, broad boulevard leading from the Tiber River to the Vatican, was jammed with people from start to end. It was a sea of flags from many nations.

Some people said they were able to sleep on their feet because the crowd was so thick.

John XXIII, who reigned from 1958 to 1963 and called the modernizing Second Vatican Council, and John Paul II, the Pole who reigned for nearly 27 years, played a leading role on the world stage.

Catholics flock to Rome

Francis' own huge popularity has added extra appeal to the unprecedented ceremony to raise two former leaders of the church to sainthood. But while both were widely revered, there has also been criticism that John Paul II, who only died nine years ago, has been canonized too quickly.

Groups representing victims of sexual abuse by Catholic priests also say he did not do enough to root out a scandal that emerged towards the end of his pontificate and which has hung over the church ever since.

The controversy has however done nothing to put off the rivers of Catholic faithful who have been arriving in Rome over the past few days.

"Pope John Paul II was the pope who opened the doors to the youth and was very close to us young people," said Argentinian nun Sister Irmana Mariella.

"I grew up with him and it is very emotional for me, especially to share and to transmit all this, personally, to all the people in Argentina who want to be here but cannot."

Security presence

Some 10,000 police and security personnel and special paramedical teams were deployed and large areas of Rome were closed to traffic.

Those pilgrims who did not want to battle the crowd spent the night praying in Rome churches left open especially for the event and would watch the event on large television screens around the city.

The election of the Argentinian-born Pope Francis has injected fresh enthusiasm into a Church beset by sexual and financial scandals during the papacy of his predecessor Benedict XVI, who last year became the first pope to resign in 600 years.

Vatican Popes Saints

Nuns wait to reach St. Peter's Square hours before the ceremony for the canonizations of Pope John XXIII and Pope John Paul II, at the Vatican, Sunday. (Riccardo De Luca/The Associated Press)

He now lives in secluded retirement but will be present at the canonization mass, which will symbolically bring together four popes. The two new saints are buried in crypts in St. Peter's Basilica.

The fact that the two being canonized are widely seen as representing contrasting faces of the Church has added to the significance of an event that Francis hopes will draw the world's 1.2 billion Catholics closer together.

John, an Italian often known as the "Good Pope" because of his friendly, open personality, died before the Second Vatican Council ended its work in 1965 but his initiative set off one of the greatest upheavals in Church teaching in modern times.

The Council ended the use of Latin at Mass, brought in the use of modern music and opened the way for challenges to Vatican authority, which alienated some traditionalists.

'Make him a saint at once'

John Paul was widely credited with helping to bring down communist rule in eastern Europe and hastening the end of the Cold War. He continued many of the reforms but tightened central control, condemned theological renegades and preached a stricter line on social issues such as sexual freedom.

A charismatic, dominant pope, he was criticized by some as a rigid conservative but the adoration he inspired was shown by the huge crowds whose chants of "santo subito!" (make him a saint at once!) at his funeral 2005 were answered with the fastest declaration of sainthood in modern history.

Both canonizations have involved some intervention with the normally strict rules governing declaration of a saint, which involve a close examination of each candidate's life and works and normally the attestation of at least two miracles.

Benedict waived a rule that normally requires a five-year waiting period before the preliminaries to sainthood can even begin to speed up John Paul's canonization, while Francis ruled that only one miracle was needed to declare John a saint.