Archbishop Eamon Martin has told a landmark Vatican summit on tackling clerical sexual abuse that testimony from abuse survivors has 'brought all of us to our knees'.

Speaking at the meeting, Archbishop Eamon Martin said: "The collective sharing here at this meeting together with the powerful testimony from victims and survivors has really brought all of us to our knees."

"I think I have been able to share with people a lot of the mistakes that we made [in Ireland], the inactions ... the very slow nature of our response at first but then to share with them the kind of systems that we have now for safeguarding in Ireland," said Dr Martin.

Archbishop Martin went on to highlight the work of the National Board for Safeguarding Children, he also spoke of the work of trained lay people in Irish parishes who are ensuring that the church is following the best safeguarding practices.

Earlier, a German cardinal said that church files on priests who sexually abused children were destroyed or never even drawn up, a move which allowed them to prey on others.

"Files that could have documented the terrible deeds and named those responsible were destroyed, or not even created," Cardinal Reinhard Marx told the summit.

"Instead of the perpetrators, the victims were regulated and silence imposed on them.

"The stipulated procedures and processes for the prosecution of offences were deliberately not complied with, but instead cancelled or overridden," he said.

Cardinal Marx was speaking on the third day of an unprecedented meeting of the world's top bishops which Pope Francis has called in an effort to get on top of a crisis that has dogged the Roman Catholic Church for decades.

The ongoing scandals have escalated to touch many countries across the globe, with cases affecting Ireland, Chile, Germany and the US.

Cardinal Marx apologised personally in September to thousands of victims of sexual assault by clergy in the German church, saying perpetrators must be brought to justice.

That followed the publication of a damning report by the German Bishops' Conference showing that almost 3,700 minors - mainly boys - were assaulted in Germany between 1946 and 2014.

The report's authors said the figure was "the tip of the iceberg".

Investigations have revealed that in many cases priests accused of assaulting minors were transferred to other parishes as bishops turned a blind eye to protect the church's reputation.

"The rights of victims were effectively trampled underfoot, and left to the whims of individuals. These are all events that sharply contradict what the church should stand for," Cardinal Marx said.

The cardinal said it was essential that victims felt "that they can trust the system".

"There are no alternatives to traceability and transparency," he insisted, adding that attempts to cover-up scandals risked seriously undermining the Catholic Church's credibility.

Pope Francis has told his bishops he wants "concrete measures" drawn up against child sex abuse, though survivor groups in Rome for the summit have accused the Vatican of fine words but little action.

The Vatican has in the past refused to hand over internal documents about child sexual abuse cases to civil authorities investigating clerical sexual abuse.

Yesterday, Archbishop Charles Scicluna, one of the Vatican's top prosecutors and an organiser of the summit, said the call for statistics to be released was "legitimate".

Earlier, an African nun criticised bishops for many mistakes in handling the sexual abuse crisis, saying the church had to acknowledge its "mediocrity, hypocrisy and complacency".

Sister Veronica Openibo, a Nigerian who has worked in Africa, Europe and the United States, had a strong message for the prelates sitting before her.

"We proclaim the Ten Commandments and parade ourselves as being the custodians of moral standards and values and good behaviour in society. Hypocrites at times? Yes! Why did we keep silent for so long?" she asked.

Sr Openibo delivered her talk at the start of the penultimate day of the summit of some 200 senior church officials.

She directly told Pope Francis, sitting near her, that she admired him because he was "humble enough to change your mind," apologise and take action after he initially defended a Chilean bishop accused of covering up abuse. The bishop later resigned.

"How could the clerical church have kept silent, covering these atrocities? The silence, the carrying of the secrets in the hearts of the perpetrators, the length of the abuses and the constant transfers of perpetrators are unimaginable," she said.

She spoke of her shock when she watched the 2015 Oscar-winning film Spotlight, which uncovered how church leaders in Boston moved predator priests from parish to parish instead of defrocking them or turning them over to civil authorities.

"At the present time, we are in a state of crisis and shame. We have seriously clouded the grace of the Christ-mission," Sr Openibo said.

"We must acknowledge that our mediocrity, hypocrisy and complacency have brought us to this disgraceful and scandalous place we find ourselves as a church. We pause to pray, Lord have mercy on us!" she said.

She said church leaders must shed their habit of hiding events for fear of making a mistake.

"Too often we want to keep silent until the storm has passed. This storm will not pass by. Our credibility is at stake".

Leading cardinals told the four-day conference yesterday that the church must repair the "systematic failures" that enabled sexual abuse to take root around the world, and bishops should start policing each other's behaviour.

At the start of the conference on Thursday, five victims told painful stories of abuse and cover-up and the pope said they could expect concrete measures to come out of the meeting.

Victims' groups have complained that while some priests who sexually abused children were eventually disciplined by the church and sentenced by civil authorities, the bishops who either enabled the abuse or covered it up have not been punished.

The conference ends tomorrow when the pope will make a final speech.

The Vatican says it will then formulate follow-up measures to make sure all bishops return home knowing how to put anti-abuse procedures into place.