Pope Francis has urged Christians to celebrate the birth of Jesus by thinking about the plight of today's children, lamenting that some must escape bombs or flee in migrant boats and how others are prevented from being born at all.

Francis celebrated a sombre Midnight Mass in a packed St Peter's Basilica, processing to the altar behind cardinals draped in golden vestments as the Sistine Chapel choir sang "Gloria" and the church bells rang out across Rome.

The Pope has spent much of the year denouncing the Islamic extremist violence that has driven Christians from Mid Eastern communities that date to the time of Christ. He has also demanded Europe in particular do more to welcome refugees, saying Jesus himself was a migrant who deserved more than being born in a manger. And he has called out the wasteful ways of the wealthy when children and the poor die of hunger every day.