Thousands of children were abused by Catholic priests in Ireland over a 30-year period, a shattering report on Church sex abuse is about to reveal.

Archbishop of Dublin Diarmuid Martin warned that a massive probe will reveal that kids were subjected to horrific attacks between 1975 and 2004.

Martin, an ex-Vatican aide, also said the full horror of those years of physical, sexual and psychological torture has not been recognized.

During Mass in Dublin's Pro-Cathedral, attended by priests from throughout the archdiocese, Martin said the report will humble the Church.

"The Archdiocese of Dublin is facing challenges of a kind that it has not experienced for many years," he said.

"The Report of the Commission on Child Sexual Abuse will shock us all.

"It is likely that thousands of children or young people across Ireland were abused by priests in the period under investigation and the horror of that abuse was not recognized for what it is."

The Dublin Archdiocese Commission of Investigation was set up in 2006 to investigate allegations of child sexual abuse involving Catholic priests in or attached to the capital's parishes.

It covers the years 1975 to 2004 and was due to report in January, but was pushed back to the summer after the state ordered allegations from the Diocese of Cloyne in Co Cork be included.

The beleaguered Bishop of Cloyne John Magee bowed to mounting pressure and stood aside last month after it was revealed he broke church rules on the handling of complaints.

A damning report released by the Catholic Church's abuse watchdog late last year found Magee took minimal action over a series of child abuse allegations against two of his priests and what little action he took was inappropriately delayed.

Between 1940 and 2008, child sex-abuse allegations have been made against 77 priests of the Dublin Diocese, while suspicions have been raised about another nine, according to official figures.

Last November, the archdiocese said there were known to be around 400 people who have made a complaint, or are known or suspected to have suffered child sexual abuse by priests.

The final number of victims is expected to run as high as the thousands.

Martin added: "The report will make each of us and the entire church in Dublin a humbler church."

Ireland was rocked by shocking revelations of clerical child abuse in 2005 when the Ferns report was published, identifying more than 100 allegations made against 21 priests between 1962 and 2002 in the Wexford diocese.

Martin was handed the task of cleaning up clerical child sexual abuse scandals in Dublin in 2004.

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