Vatican City: Pope Francis urged the world to let the light of Christmas pierce the "darkness in human hearts" that leads to religious persecution, social injustice, armed conflicts and fear of migrants.

In his "Urbi et Orbi" (to the city and the world) Christmas Day message, the 83-year-old Pope called for peace in the Holy Land, Syria, Lebanon, Yemen, Iraq, Venezuela, Ukraine and several African countries caught up in conflicts.

Pope Francis waves to the crowd after delivering the Christmas day blessing. Credit:AP

The common thread of his address to tens of thousands of people in St Peter's Square and millions watching or listening around the world was that change starts in the hearts of individuals.

"There is darkness in human hearts, yet the light of Christ is greater still," Francis said, as he marked the seventh Christmas of his pontificate.