A notorious paedophile priest abused every boy at a regional Victorian school between the age of 10 and 16, the child sex abuse inquiry has heard.

The Royal Commission into Institutional Responses to Child Sexual Abuse is holding long-awaited public hearings in Ballarat to examine historical abuse suffered by children at a number of schools in the regional centre, at the hands of Catholic clergy and other members of the Church.

Some of Australia's most notorious abusers, including Gerald Ridsdale, Robert Best and Edward Dowlan, were part of a paedophile ring operating in and around Ballarat for years.

In her opening address, Senior Counsel Assisting the Commission, Gail Furness SC, outlined the extent of Ridsdale's offending.

She said the inquiry would hear evidence of Ridsdale's time at the Mortlake parish during the early 1980s, including comments from the priest who took over from Ridsdale.

"Father Dennehy told the Catholic Church's insurance investigator that he thought every male child between the ages of 10 years and 16 years, who were at the school, had been molested by Ridsdale," she said.

Ms Furness said Ridsdale was a "prolific offender" during his time at Mortlake.

"There will be evidence that his behaviour around boys was no secret," she said.

She also told the inquiry Cardinal George Pell - who later became Archbishop of Sydney and now oversees the Vatican's finances - was one of seven present at a meeting in September 1982 where Bishop Ronald Mulkearns discussed the need to remove Ridsdale from the school.

She said under the heading of "staff" the notes from that meeting read:

The Bishop advised that it had become necessary for Father Gerald Risdale to move from the Parish of Mortlake. Negotiations are under way to have him work with the Catholic Enquiry Centre in Sydney. A new appointment to Mortlake will be necessary to take effect after October 17th.

The minutes did not disclose whether the Bishop said why the move was necessary, she told the inquiry.

"However ... it is expected that there will be evidence that Bishop Mulkearns knew it was because Ridsdale had abused boys in Mortlake and that he had offended in this manner in 1975," she said.

All male teachers at St Alipius PS were molesting

Ballarat was one of the most horrific sites of abuse and it was revealed that in 1971, all male teachers and the chaplain at the St Alipius primary school were molesting children.

It was revealed that in 1971 all male teachers and the chaplain at the St Alipius primary school were molesting children. ( Supplied: Catholic Church )

Ms Furness said the royal commission would also hear from a survivor who had a photograph of his grade four class at St Alipius in the 1970s.

She said he would tell the hearing, of the 33 boys pictured, 12 had committed suicide.

In his opening address, inquiry chairman Justice Peter McClellan urged those attending the hearing to remember the victims and survivors.

"The evidence in the first stage of this hearing will include the personal stories of a number of survivors," Justice McClellan said.

"That evidence will describe the gross violations of individuals by ordained members of the Catholic Church.

"As you are aware, the royal commission has revealed many shocking stories of the betrayal of children.

"As we listen to the evidence in this hearing, we should all reflect on the impact for those who have suffered in the Ballarat region, and the thousands of others who have suffered throughout Australia."

Ridsdale to give evidence to inquiry via video link from prison

Justice McClellan said the inquiry would also hear from perpetrators but not directly about the circumstances of their offending.

"That has already been dealt with by the courts," Justice McClellan said of Ridsdale's crimes.

"However, the evidence has an important part to play in the royal commission coming to understand both the way ordained members of the Catholic Church became abusers and how the Church responded to allegations of their abuse."

Ridsdale is serving an eight-year prison sentence after pleading guilty to 30 child sex offences in 2014.

It is the fourth time he has been jailed after three previous stints in prison for more than 100 other offences.

He will give evidence, possibly next week, via video link from prison.

The hearing will also consider why Ridsdale was able to move around to so many locations in Victoria, without being reported to police.

He offended and re-offended in Horsham, Inglewood, Camperdown, Ballarat North, Mildura, Swan Hill, Warrnambool, Ballarat East, Apollo Bay, Edenhope, Melbourne and Mortlake.

"I appreciate that the evidence of perpetrators may be confronting for some people, in particular survivors," Justice McClellan said.

"However, without the evidence of perpetrators the true story of the response of the Church in Ballarat may never be completely revealed.

"I am aware that there may be different and strongly held views about the conduct of ordained people and the appropriateness of the response of leaders in the Church in the Ballarat Diocese.

"Many want this hearing. There are others who doubt the need for a public hearing. Some may not want the story told.

"Unless the truth is revealed and known publicly then [the] prospect of effective healing for survivors and institutions is diminished."

Support on hand as inquiry prepares for gruelling three weeks

Today's hearing was packed with survivors and their supporters and a spill-over court was set up in an adjacent building to cope with demand.

Justice McClellan said support would be on hand for survivors as the hearing progressed.

The Catholic Church also warned of a gruelling few weeks of evidence.

Bishop of Ballarat Paul Bird released a statement urging people across the region to support one another throughout the hearing.

He will also give evidence, as will Brother Peter Clinch, the Province Leader of the Christian Brothers Oceania Province.

Former Bishop Ronald Mulkearns, who is accused of moving perpetrators and destroying documents to avoid detection, is not on the witness list.

He did not appear before the Victorian parliamentary inquiry into child sex abuse, citing ill health.

Ms Furness said 17 abuse victims would give evidence and the commission would also hear from a psychiatrist about the post-traumatic effects of child abuse on survivors.

Some victims will give evidence anonymously, under a pseudonym.

"Many witnesses are expected to say that they were reluctant to disclose their abuse to anyone," Ms Furness said.

"They are expected to give reasons such as feelings of shame, guilt, disgust, fear of punishment, fear of judgment and a belief that they would be disbelieved."

Perpetrators must be called to account, victims say

Abuse victim Patrick Nagle, 50, of Ballarat, was abused at St Alipius and said testifying before the commission was "extremely difficult".

"We've known this has been coming for about three months and I haven't slept [the] last couple of nights," he said.

"You've got to prepare yourself for it.

"[It was] very, very tough indeed, but [I'm] glad it's over [I'm] going to go and have a beer now."

Andrew Collins, 46, of Mount Helen, was abused by four different men at Ballarat schools and churches during his teenage years.

He said it was important that those who moved these men around and did not report the abuse to police were brought to justice.

"It's not just the perpetrators, it's the hierarchy that facilitated those abusers to cause so much more hurt, pain and suffering," he said.

Mr Collins said the number of victims who had committed suicide was "horrendous".

"There's been over 40 confirmed suicides where suicide notes have been linked to the abuses, but we're aware of many other victims who have taken their own lives," he said.

"We've had 10 [suicides] in the last 12 months and it is just painful and horrendous to open up the newspaper and see that somebody you know, you know was abused, hasn't told their family, has taken their own life."