Attorney-General Nicola Roxon said it was "abhorrent" for priests not to report paedophilic acts revealed in the confessional.

Australia has announced a royal commission into how religious organisations, not-for-profit bodies, state agencies, schools and police have responded to child sex abuse in a wide-ranging inquiry set to take years.

Roxon said one of the issues it could consider was whether the protection of the confessional should be removed.

"I think the royal commission needs to look very carefully... at institutional barriers, at systematic problems, of course that might include those very sensitive issues for religious organisations," she said.

The country's most senior Catholic clergyman, Sydney Archbishop George Pell, said Tuesday the confessional remains "inviolable" and could not be broached.

But Roxon, when asked whether it would be right for priests to respect the confidentiality of the confessional in the case of child sex crimes, said: "I think the whole community finds that idea really abhorrent.

"We've been through these debates for mandatory reporting for doctors, for teachers," she told state broadcaster ABC.

"So I think we really need to look carefully; there aren't a different set of rules that apply. Child sexual abuse is a crime, it should be reported. We can't afford to say that that is not on the table."

New South Wales state Premier Barry O'Farrell, who has called for a probe into recent allegations of a cover-up of child sex abuse among Catholic clergy in the Hunter Valley, north of Sydney, also said mandatory reporting was needed.

"How can you possibly, by the continuation of this practice, potentially continue to give, if not a green light, a free pass to people who've engaged in the most heinous of acts?" he said.

The government has indicated that the inquiry will be extensive, requiring several commissioners and likely to take a number of years, as did Ireland's Commission to Inquire into Child Abuse, which took close to a decade.