The royal commission investigating institutional responses to child sex abuse has handed down its interim report, but says it has not yet compiled enough information to make any recommendations.

It is calling for an additional two years and $104 million in extra funding to complete the 70 public hearings they have identified as "essential".

So far, only 13 of the hearings have been held. The commission has also conducted thousands of private sessions with individuals, but it says there are around 3,000 more on a waiting list.

The interim report says that despite legal obligations to report child abuse, it remains significantly under-reported in Australia.

The royal commission says it has identified several main themes from the many personal stories it has heard.

The themes include repeated abuse and multiple perpetrators, barriers to reporting the abuse and adults that have systematically failed to protect children.

However, it says it is not clear how prevalent abuse has been, or continues to be, in institutions.

The report says pre-employment screening is not consistent across the nation, and the royal commission is investigating if a national screening agency and stronger laws are the answer.

Attorney-General George Brandis says the report, which was tabled in Parliament today, is an important milestone for the commission and the Australian community.

"The interim report makes clear the enormous scale of the task being undertaken by the commission," he said.

Reporter Emily Bourke has told PM the report is two volumes and 700 pages. Volume one is a description of the work done by the royal commission so far, the issues that the commission is examining, and the work that still needs to be done. Volume two is a representative sample of the 150 personal stories from people who've shared their experience at a private session. The royal commission has held about 1,700 private sessions. There's been 96 days of public hearings and 220 witnesses. By May of this year more than 160 allegations were referred to police. The commission needs to hear from about 4,000 people in private sessions and that won't be achieved by its initial reporting deadline of 2015. So it's asked for another two years. The royal commission says the public airing of these case studies has led to some change. Child protection agencies and faith-based institutions are reviewing the way they hire people, the Catholic and Anglican churches are sharing information on governance and finances in a way that they never have before, and institutions are reviewing their attitude to accepting responsibility for the criminal acts of their staff. Listen to the full interview here.

Senator Brandis says the request for an extension is under consideration by the Government.

The chief executive of the Catholic Church's Truth, Justice and Healing Council, Francis Sullivan, is backing the commission's call for an extension.

"It's essential ... this is the opportunity for our community to get to the real reasons why children haven't been safe in institutions," he said.

The interim report outlines a number of findings, with the commission's initial research showing 90 per cent of perpetrators were male.

It has found that it took 22 years on average for victims to report abuse, with men taking longer than women.

It says female victims were, on average, aged nine years old and took, on average, 22 years to report abuse.

Male victims were, on average, 10 years old when they were abused.

The creation of the royal commission was announced by former prime minister Julia Gillard in November 2012.

Ms Gillard said there had been too many revelations of "adults who have averted their eyes" from the evil of child sexual abuse.

"Australians know... that too many children have suffered child abuse, but have also seen other adults let them down - they've not only had their trust betrayed by the abuser but other adults who could have acted to assist them have failed to do so," she said at the time.