A former Vatican archbishop accused of paedophilia stored tens of thousands of child porn videos and photos on a computer in his office at the Holy See diplomatic compound in the Dominican Republic, it has emerged.

Details of Jozef Wesolowski's massive child porn stash have been revealed after the 66-year-old was arrested at the Vatican earlier this week.

He is the highest-ranking Vatican official ever to be investigated for sex abuse, and the first top papal representative to receive a defrocking sentence. He has been charged with sexually abusing minors and child porn possession and might face up to seven years in the Vatican's tiny jail.

Vatican detectives analysed the PC Wesolowski used in his office in Santo Domingo, where he served as Holy See envoy from 2008 to 2012 as part of an investigation into the alleged sexual abuse of underage boys.

The probe reportedly revealed a collection of horrors. The Polish native held more than 100,000 sexually-explicit files, Il Corriere della Sera newspaper reported.

Some 160 videos showing teenage boys forced to perform sexual acts on themselves and on adults and more than 86,000 pornographic photos were meticulously archived in several category-based folders, the paper said.

Investigators said that at least another 45,000 pictures were deleted, while a second stash of material was found on a laptop Wesolowski used during his trips abroad.

The former clergyman was placed under house arrest in a pre-trial detention at the Vatican earlier this week. He has been detained in a small room in the basement of the Collegio dei Penitenzieri, a convent located in the same building hosting the Vatican's court and military police in the famous Santa Marta square.

Investigators are also probing whether there was a network of people who helped him to set up sexual encounters and if he committed other abuse during his previous posts around the world.

Before arriving in Santo Domingo, Wesolowski served as apostolic nuncio in Bolivia and Central Asia - covering Kazakhstan, Tajikistan, Kirghizstan and Uzbekistan - after holding less prominent roles in Southern African, Costa Rica, Japan, Switzerland, India and Denmark.

He was recalled to Rome last year, after Dominican Republic media alleged he hired "rent boys" and was subsequently banished from the clergy, after a canonical court found him guilty of sex abuse.

His trial is expected to start in January.