FATIMA, Portugal (Reuters) - Pope Francis, visiting one of Catholicism’s most famous sanctuaries, on Friday prayed for an end to wars he said were lacerating the world and urged the faithful to “tear down all walls” to spread justice and peace.

At the start of a trip that will see him on Portuguese soil for less than 24 hours, Francis arrived at the Shrine of Fatima, where the Catholic Church teaches that the Madonna appeared to three Portuguese children 100 years ago in what was then an impoverished farming village.

The main purpose of the trip to the central Portuguese town, which receives around 7 million people a year, is a huge open-air Mass on Saturday to declare two of the children saints.

The two, Francisco and Jacinta Marto, died shortly after the apparitions at the ages of 9 and 10. The third visionary, Lucia Dos Santos, became a nun and died in 2005 at the age of 97.

Watched by hundreds of thousands of people, Francis read a long prayer before a small statue of the Madonna, leaving a gold rose at her feet.

“I implore for the world concord among all peoples” he said, decrying blood “shed in the wars tearing our world apart”.

Since his election in 2013, Francis has made hundreds of appeals for peace, including calling for international mediation to reduce tensions between the United States and North Korea.

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A banner in the crowd read: “Please pray for peace in Korea”.

In his prayer, which the huge crowd listened to in near silence, Francis also hammered home another major theme of his papacy - justice for the poor, refugees and outcasts.

“We will follow all paths and everywhere make our pilgrim way; we will tear down all walls and cross every frontier as we go out to every periphery to make known God’s justice and peace,” he said.

The story of Fatima’s shepherd children has captivated Catholics since their first reported vision on May 13, 1917.

The Church believes the Madonna gave the children three messages, the so-called secrets of Fatima.

The first two were revealed soon and concerned a vision of hell, seen by believers as a prediction of the outbreak of World War Two, a warning that Russia would “spread her errors” in the world, and a need for general conversion to God and prayer.

The “third secret” intrigued the world for more than three-quarters of a century, inspiring books and cults convinced that it predicted the end of the world.

In 2000, the Vatican said it was a prediction of the 1981 assassination attempt on Pope John Paul on May 13, the same day of the first reported apparition in 1917.

John Paul believed the Madonna had diverted one of the bullets that hit him from his vital organs. He donated it to the sanctuary, where it is now embedded in the crown of the statue that Francis prayed before on Friday night.