The reach of laws against female genital mutilation (FGM) will be tested in the High Court today, as it considers calls for a retrial of three people accused of carrying out a practice known as Khatna on two young sisters in Wollongong.

Key points: The High Court will be asked to determine what constitutes genital mutilation

The High Court will be asked to determine what constitutes genital mutilation The appeal stems from Australia's first prosecution on the matter

The appeal stems from Australia's first prosecution on the matter The defence argues no visible damage was done to the girls, and thus they were not mutilated

Former nurse Kubra Magennis and a Dawoodi Bohra community leader, Shabbir Mohammedbhai Vaziri, were found guilty along with the girls' mother of breaching the law in 2015.

It was Australia's first female genital mutilation prosecution.

WARNING: This story contains graphic details that may be confronting to some readers.

But the charges were quashed last year by the New South Wales Court of Appeal after new evidence that there was no visible physical damage to either girl.

Khatna is said to involve a girl's clitoris being nicked or cut during a ceremony in the presence of elders.

In the months after the trio's conviction, a medical examination showed the tip of the clitoral head was visible in both girls, excluding the possibility that it had been removed.

But prosecutors will tell the High Court today the actions of the three still breached the NSW law against FGM and should be retried.

The girls are believed to have been aged six or seven when the Khatna ceremony was carried out on separate occasions at their homes, once in Wollongong and the other in Sydney between 2009 and 2012.

At the original trial, the two women were found guilty of mutilating the girls' genitals, and Mr Vaziri of being an accessory for encouraging community members to lie about the procedure.

The court will consider whether mutilation can be proved when no visible damage was done. ( AAP: Dan Himbrechts )

The eldest child gave evidence describing the practice, saying "they give a little cut … in your private part".

She said she was not used to talking about it because her mother had told her not to go around telling everyone.

At the trial, she said she had seen Ms Magennis with "a silver toolish thing" which looked similar to a pair of scissors.

Ms Magennis has maintained they were forceps, and that the symbolic form of Khatna involved a "ceremony of touching the edge of the genital area … allowing the skin to sniff the steel".

At the 2015 trial, the defence argued this was only done with forceps, and the girls were not cut.

The New South Wales Crimes Act outlaws conduct that "excises, infibulates or otherwise mutilates" the external genitalia of a woman or girl without a valid healthcare reason.

The key issue in the High Court challenge will be the interpretation of the term "otherwise mutilates", given the girls involved suffered no visible damage.

Prosecutors will argue the term covers the actions of the trio, and that they should be retried.