The 82-year-old pontiff announced the changes in the centuries-old Rosary in his weekly audience, simultaneously issuing a special document.

John Paul proclaimed the start of the Year of the Rosary and urged Catholics to take advantage of the new focus on the Rosary to revive their faith and flagging practice of the set of prayers.

"We must rediscover the profound mysticism contained in the simplicity of this prayer, dear to popular tradition," the pope told thousands of pilgrims and tourists in St. Peter's Square.

The Rosary is a series of prayers, many dedicated to the Virgin Mary, that are recited over and over again with the help of sets of beads that the faithful hold.

Traditionally, Catholics are supposed to contemplate three periods, or mysteries, of Christ's life as they recite the prayers: the joyous mysteries of his birth, the sorrowful mysteries of his crucifixion, and the glorious mysteries of his resurrection.

On Wednesday, John Paul proposed adding another set of mysteries: the "mysteries of light," which highlight five different periods of Christ's life.

"This addition of these new mysteries, without prejudice to any essential aspect of the prayer's traditional format, is to give it fresh life and to enkindle renewed interest in the Rosary's place within Christian spirituality," the pope wrote in his apostolic letter.

The pope, who has dedicated his papal motto to the Virgin Mary, is particularly devoted to the Rosary, which he has called his favourite prayer.

On Wednesday, many of the faithful in St. Peter's Square clutched Rosary beads, and the Hail Mary -- one of the main prayers of the Rosary -- was recited en masse.

The pope's anniversary was a Vatican holiday. John Paul opened his anniversary audience by praying to Mary and asking she help him carry on his mission.

John Paul is already one of the longest serving popes in history and despite suffering increasing infirmity has outlived many of those seen as possible successors.

Although he suffers from Parkinson's disease well as knee and hip problems, he has made it clear he has no intention of stepping down.

"It's the start of the 25th year of John Paul's pontificate," the Vatican newspaper L'Osservatore Romano declared in a special edition, as if to emphasise the pope's resolve.

The Vatican issued a spate of statistics to show the records of his papacy -- including 98 foreign trips covering 1.24 million kilometres (742,020 miles), elevating 464 saints and holding 1,430 audiences and meetings with political leaders.

Only four popes have served longer than John Paul, and he is closing in on two of them. By Vatican count, the record is held by St. Peter, the first pope, listed as serving either 30 or 37 years.

Although a proposed trip to the Philippines in January has been ruled out, a sign that John Paul is slowing down, Vatican officials insist that the most travelled pope in history will continue foreign pilgrimages with a visit to Croatia next spring.