Catholic leader tells stony-faced cardinals, bishops and priests of church's "15 ailments" in unusual address.

Pope Francis has harshly criticised Vatican bureaucracy in a Christmas speech, saying that some in the Church suffered from "spiritual Alzheimer's" and a lust for power.

Vatican watchers said they had never heard such a powerful, violent speech from a pope and suggested that it was informed by the results of a secret investigation ordered up by Emeritus Pope Benedict XVI in the aftermath of the 2012 leaks of his papers. 

Francis told cardinals, bishops and priests on Monday the Vatican was riven with "existential schizophrenia", "social exhibitionism", "spiritual Alzheimer's" and a lust for power, all of which made for an "orchestra that plays out of tune". 

"The Curia is called on to always improve itself and grow in communion, holiness and knowledge to fulfill its mission,'' Francis said. 

"But even it, as any human body, can suffer from ailments, dysfunctions, illnesses." 

In a speech that was met with tepid applause when it ended, the pope listed one by one the 15 "Ailments of the Curia" that he had drawn up, complete with footnotes and Biblical references. 

The Catholic pope started off his list with the "ailment of feeling immortal, immune or even indispensable.'' 

Then one by one he went on: Being rivals and boasting. Wanting to accumulate things. Having a "hardened heart.'' Wooing superiors for personal gain. Having a "funereal face'' and being too "rigid, tough and arrogant,'' especially toward underlings. 

Francis spoke of the "terrorism of gossip" saying backstabbing by "cowards who don't have the courage to say things openly" is tantamount to "murder in cold blood. 

He bemoaned the "scandal" caused by infighting and those who use their Vatican careers to grab power and wealth, of living "hypocritical" double lives and forgetting that they're supposed to be joyful men of God. 

The leader of the world's 1.2 billion Roman Catholics also warned against greed, egoism and people who think they are "immortal". 

Francis turned the traditional, genteel exchange of Christmas greetings into a public dressing down of the Curia, the central administration of the Holy See, which governs the 1.2-billion strong Catholic Church. 

He made clear that his plans for a radical reform of the structures of church power must be accompanied by an even more radical spiritual reform of the men involved. 

Despite winning the hearts of many religious and non-religious people alike, the pope has also made enemies, particularly within the conservative arm of the Church. 

The Argentine pope's attempts to kick-start dialogue within the Church earlier this year over a possible new approach to remarried, divorced people and homosexuals sparked an outcry in some quarters.