Pope Francis has urged the world's Catholics to remember the poor and war-weary, saying in an apparent reference to the war in Ukraine and other conflicts that the level of greed and hunger for power was such that some wanted to "consume even their neighbours".

The pope, celebrating the 10th Christmas of his pontificate, delivered his comments on Saturday at a solemn Christmas Eve Mass in St Peter's Basilica.

It was the first with a capacity crowd of about 7,000 following several years of restricted attendance because of COVID.

About 4,000 other people participated outside in St Peter's Square on a relatively warm night.

As has been the case for the past several months, a knee ailment prevented the pope from standing for long periods, with a cardinal delegated to be the main celebrant at the altar of the largest church in Christendom.

Sitting to the side of the altar for most of the Mass, Pope Francis wove his homily around the theme of greed and consumption on various levels, asking people to look beyond the consumerism that has "packaged" the feast, rediscover its meaning, and remember those suffering from war and poverty.

"Men and women in our world, in their hunger for wealth and power, consume even their neighbours, their brothers and sisters," he said.

Since Russia invaded its neighbour in February, the pope has spoken out against the war at nearly every public event, at least twice a week, denouncing what he has called atrocities and unprovoked aggression.

He did not specifically mention Ukraine on Saturday night.

"As always, the principal victims of this human greed are the weak and the vulnerable," he said, denouncing "a world ravenous for money, power and pleasure…"

"I think above all of the children devoured by war, poverty and injustice," also mentioning "unborn, poor and forgotten children".

Drawing a parallel between the infant Jesus born in a manger and the poverty of today, the pope said: "In the manger of rejection and discomfort, God makes himself present. He comes there because there we see the problem of our humanity: the indifference produced by the greedy rush to possess and consume."

Earlier this month, the pope urged people to spend less on Christmas celebrations and gifts and send the difference to Ukrainians to help them get through the winter.

The pope marked his 86th birthday last week and, apart from the knee ailment, appears to be in overall good health.

On Christmas Day, he is due to deliver his twice-year "Urbi et Orbi" (to the city and the world) blessing and message from the central balcony of St Peter's Basilica to tens of thousands of people in the square below.

Reuters