Pope Francis warned against a society "intoxicated by consumerism" as he celebrated Christmas Eve Mass at the Vatican.

Children were at the heart of the Christmas celebration in St Peter's Basilica, and some youngsters invited to attend came from countries that Pope Francis has visited as pontiff.

The children left floral bouquets around a baby Jesus statue near the central altar after the pope unveiled and gently kissed the statue.

The basilica's bells rang at the start of the late-night ceremony, which is Pope Francis' only public Mass for Christmas. Hymns were played on trumpets.

In his homily, delivered in Italian, the pope said: "Today, the Son of God is born, and everything changes.

"The saviour of the world comes to partake of our human nature; no longer are we alone and forsaken.

"In a society so often intoxicated by consumerism and hedonism, wealth and extravagance, appearances and narcissism, this child calls us to act soberly, in other words, in a way that is simple, balanced, consistent, capable of seeing and doing what is essential.

"In a world which all too often is merciless to the sinner and lenient to the sin, we need to cultivate a strong sense of justice, to discern and to do God's will.

"Amid a culture of indifference which not infrequently turns ruthless, our style of life should instead be devout, filled with empathy, compassion and mercy, drawn daily from the wellspring of prayer."

Today, tens of thousands of people are expected to flock to St Peter's Square outside the basilica to hear the pontiff deliver a traditional speech at noon.