An organiser of this week's summit of Catholic Church leaders on clerical child sexual abuse has warned that silence about the scandal is a "no-go" option.

Archbishop Charles Scicluna also told hundreds of journalists in the Vatican that church leaders have to face the facts because only the truth will make the church free.

With three days to go before Pope Francis convenes more than 200 church leaders, including one from virtually every country in the world, a packed news conference heard from the organisers what the Pontiff is hoping to achieve.

One reporter asked why it had had taken this long for the church to ensure that every bishop knows what to do about clergy who abuse children.

Archbishop Scicluna said: "The first immediate response is almost to deny what has happened, so denial is such a natural response, but it's not sufficient. It's a primitive mechanism that we need to move away from.

"And so whether it's criminal or malicious complicity on a code of silence, so whether it's denial, which is trauma in its very primitive state, we need to go away from that.

"That's why the third day of this important meeting is going to be on transparency, this needs to break any code of silence, any complicity with denial."

Meanwhile, the Archbishop of Dublin, who has not been invited to the summit, told RTÉ News that many people are asking why it took until last week the Vatican to expel disgraced US Cardinal, Theodore McCarrick.

McCarrick was removed from from the priesthood following findings that he had sexually abused children and seminarians for decades.

Diarmuid Martin underlined that one of his former bosses in his former post in the Vatican had also been disciplined last week.

The Irish church is being represented at the summit by the Primate of All Ireland and Archbishop of Armagh Eamon Martin.

The senior bishops are gathering this week for the conference that is designed to guide them on how best to tackle a problem that has decimated the church's credibility, but critics say it is too little, too late.

The four-day meeting, starting on Thursday, brings together presidents of national Catholic bishops conferences, Vatican officials, experts and heads of male and female religious orders.

"I am absolutely convinced that our credibility in this area is at stake," said Fr Federico Lombardi, who Pope Francis has chosen to moderate the meeting.

"We have to get to the root of this problem and show our ability to undergo a cure as a church that proposes to be a teacher or it would be better for us to get into another line of work," he told reporters.

The church has repeatedly come under fire for its handling of the sexual abuse crisis, which exposed how predator priests were moved from parish to parish instead of being defrocked or turned over to civilian authorities around the world.

The pope called the meeting in September at the suggestion of his closest advisers.

Last month, he told reporters it was necessary because some bishops still did not know fully the procedures to put in place to protect the young and how to administer cases of abuse.

Pope Francis said it would be a "catechesis," or a teaching session, a pronouncement that stunned victims of abuse and their advocates.

Some experts have questioned why it has taken so long to get to this point.

"The fact that this still exists in 2019, that there is still awareness-raising that has to be done (among bishops) is a measure of what a low priority this has truly been for the Vatican," said Anne Barrett-Doyle of the US-based abuse tracking group

"I hope he has the candour to admit that it's absolutely disgraceful that that's where we are today," said Ms Barrett-Doyle.

Additional reporting: AFP