Ms Roxon said the government was keen to discuss with the states ''whether there are advantages to doing it jointly and whether there's an interest in doing so''.

It was common in the 1970s and 1980s to have the Commonwealth and a number of states jointly establish commissions that were looking at issues that crossed jurisdictional boarders, she said.

A joint inquiry might make it easier to overcome the issue of split power and could better integrate the inquiries being done at state level.

Ms Roxon said the issue of whether priests should have to report sex abuse crimes discussed in the confessional needed to be examined. ''Child sexual abuse is a crime. It should be reported,'' she said. Cardinal George Pell this week said ''The seal of confession is inviolable''.

Asked whether the commission should examine removing that seal, Prime Minister Julia Gillard said: ''Adults have got a duty of care towards children, and it's not good enough for people to engage in sins of omission and not act when a child is at risk.''

Opposition Leader Tony Abbott said, ''everyone has to obey the law … If they become aware of sexual offences against children, those legal requirements must be adhered to.''

People had to obey regardless of what job they were doing, or what position they held. That included priests, he said. But he did not say whether the law should or should not exempt priests hearing confessions.

Professor of law at the Australian Catholic University Father Frank Brennan said he had been a priest for 27 years, including many years at Kings Cross, and had never had anyone confess to child abuse.

He thought confessional privilege should stay. If the law was changed, he said he would not breach the confidentiality of people and, if necessary, he would go to jail.

Liberal frontbencher Christopher Pyne, a Catholic, said: ''The simple reality is that if a priest hears from another priest in the confessional that they are an abuser of children, I think they have an obligation to report that to the authorities.''