Police have charged Pope Francis's top financial adviser - Australia's most senior Vatican clergyman - with historical sex offences.

Cardinal George Pell, who is one of the most high-ranking Catholic officials, faces multiple charges of assault involving several complainants.

Australian police reported on Thursday that Pell had been summoned to the country to face the accusations.

He has now become the highest-ranking Vatican official to ever be charged in the Catholic church's long-running sexual abuse scandal.

Victoria state Police Deputy Commissioner Shane Patton said that Pell faced several charges related to "historic sexual offences".

No further details about the allegations, except that they involved a number of alleged victims, were given.

Pell has repeatedly denied all abuse allegations made against him.

The latest development will come as a further blow for Pope Francis, who has promised a "zero tolerance" policy towards sex abuse.

Pell had already faced allegations for years that he mishandled cases of clergy abusing children while he was an archbishop in both Melbourne and Australia.

Only last year, he acknowledged during a testimony that the Catholic Church had made "enormous mistakes" by allowing thousands of children to fall victim to rape and molestation by priests.

And he admitted that he too had often believed priests over victims who claimed to have been abused.

Pell has been summoned to appear before a Melbourne court on July 18.