Pope Francis has urged people to see differences as a source of richness instead of danger and has used his Christmas message to call for reconciliation in places torn apart by conflict.

Pope Francis delivered the traditional papal "Urbi et Orbi" message to tens of thousands of people in a sunny St Peter's Square from the same basilica balcony where he first appeared as pontiff shortly after his election on 13 March 2013.

Security has been tight around the Vatican for the Christmas season, with military jeeps stationed at key access routes and tourists undergoing metal detector and bag searches.

In his address, in what appeared to be a reference to the shrill political climate in a number of countries, Pope Francis called for "fraternity among people with different ideas, yet capable of respecting and listening to one another".

Pope Francis, the first pope from Latin America, alluded to polarisation over migration, saying God wanted "love, acceptance, respect for this poor humanity of ours, which we all share in a great variety of races, languages, and cultures".

"Our differences, then, are not a detriment or a danger; they are a source of richness," he said.

The 82-year-old also called for the resumption of dialogue between Israelis and Palestinians to "undertake a journey of peace that can put an end to a conflict that for over 70 years has lacerated the land chosen by the Lord to show his face of love".

He urged the international community to work for a political solution in Syria and said he hoped a truce brokered in Yemen's civil war could bring relief to a population exhausted by violence and famine.

The Argentinian-born pope also called for social harmony in Nicaragua and Venezuela, both racked by internal political conflicts.

The millions of refugees or displaced people in Africa who are in need of humanitarian assistance and food security should not be forgotten, he said.

In Ukraine, he called for "a peace respectful of the rights of every nation".

Last night, Pope Francis criticised the "insatiable greed" of today's consumerism, using his Christmas homily to call on people to make "sharing and giving" more a part of their lives.

"Mankind became greedy and voracious," the leader of the world's 1.3 billion Catholics said in an address to thousands of followers in Saint Peter's Basilica in Rome.

"In our day, for many people, life's meaning is found in possessing, in having an excess of material objects," he said.

"An insatiable greed marks all human history, even today, when, paradoxically, a few dine luxuriantly while all too many go without the daily bread needed to survive."

The birth of Christ pointed to a new way to live "not by devouring and hoarding, but by sharing and giving", he said during a Christmas Eve mass.

We "must not lose our footing or slide into worldliness and consumerism," he added.

People should ask themselves: "Do I really need all these material objects and complicated recipes for living? Can I manage without all these unnecessary extras and live a life of greater simplicity?" he asked.