A senior Vatican cardinal charged in Australia with multiple historical sexual offences has denied the accusations and denounced what he called a "relentless character assassination" in the media.

Cardinal George Pell, Pope Francis's chief financial adviser and Australia's most senior Catholic, said he would take a leave of absence as the Vatican's finance tsar and would return to Australia to fight the charges.

Pell is the highest-ranking Vatican official charged in the church's long-running sexual abuse scandal.

Deputy Commissioner Shane Patton of Victoria state police said officers have summonsed Pell to appear in court to face multiple charges of historical sexual assault offences.

Mr Patton gave no other details of the allegations. Pell was ordered to appear at Melbourne Magistrates' Court on July 18.

Pell, 76, has for years faced allegations that he mishandled cases of clergy abuse when he was archbishop of Melbourne and then Sydney, but more recently, he became the focus of a sex abuse investigation himself, with Victoria detectives flying to the Vatican last year to interview him.

It is unclear what allegations the charges relate to, but two men, now in their 40s, have said Pell touched them inappropriately at a swimming pool in the late 1970s when he was a senior priest in Melbourne.

Mr Patton told reporters in Melbourne that none of the allegations against Pell had been tested in any court, adding: "Cardinal Pell, like any other defendant, has a right to due process."

The charges are a new and serious blow to Pope Francis, who has already suffered several credibility setbacks in his promised "zero tolerance" policy about sex abuse.

The charges also complicate Francis's financial reform efforts at the Vatican, which were already strained by Pell's repeated clashes with the Italian-dominated bureaucracy.

Last week, one of Pell's top allies, the Vatican's auditor general, resigned without explanation two years into a five-year term, raising questions about whether the reform effort was doomed.

Vatican spokesman Greg Burke said Pope Francis had learned with "regret" of the charges and had granted Pell a leave of absence to defend himself. He said the Vatican's financial reforms would continue in his absence.

Pell's actions as archbishop have come under intense scrutiny in recent years by a government-authorised investigation into how the Catholic Church and other institutions have responded to the sexual abuse of children.

Australia's Royal Commission into Institutional Responses to Child Sexual Abuse - the nation's highest form of inquiry - has found shocking levels of abuse in Australia's Catholic Church, revealing earlier this year that 7% of Catholic priests had been accused of sexually abusing children over the several decades.

Last year, Pell acknowledged during evidence to the commission that the Catholic Church had made "enormous mistakes" in allowing thousands of children to be raped and molested by priests over centuries.

He conceded that he had erred by often believing priests over those who alleged abuse, and he vowed to help end a rash of suicides among church abuse victims in his home town of Ballarat.

Francis appointed Pell in 2014 to a five-year term to head the Vatican's new economy secretariat, giving him broad rein to control all economic, administrative, personnel and procurement functions of the Holy See. The mandate has since been restricted to performing more of an oversight role.