Pope Francis has urged Roman Catholics not to ignore the plight of millions of migrants "driven from their land", during Christmas Eve Mass.

The pontiff compared them to Mary and Joseph, recounting the Biblical story of how they travelled from Nazareth to Bethlehem but found no place to stay.

Many migrants, he said, were being forced to flee from leaders who "see no problem in shedding innocent blood".

He has made defence of migrants around the world a major theme of his papacy.

The number of refugees worldwide exceeds 22 million, with the latest cross-border influx being the Rohingya fleeing violence in Myanmar.

"So many other footsteps are hidden in the footsteps of Joseph and Mary," the 81-year-old Argentine pontiff, himself the grandson of Italian migrants, told worshippers in St Peter's Basilica in the Vatican City on Sunday evening.

"We see the tracks of millions of persons who do not choose to go away but, driven from their land, leave behind their dear ones."

The leader of the world's estimated 1.2bn Roman Catholics also stressed that faith demanded that foreigners be welcomed everywhere.

The Pope will give his traditional "Urbi et Orbi" ("to the city and to the world") Christmas address later on Monday.