A man accused of sexually assaulting a seven-year-old girl in Sydney's south will remain behind bars.

A convicted rapist has admitted he sexually assaulted a seven-year-old girl he had choked and held at knifepoint in a Sydney dance studio bathroom.

Anthony Peter Sampieri, 55, on Thursday pleaded guilty to three counts of child rape and seven other charges in Sydney’s Central Local Court.

It related to his brutal attack on the child at the dance studio where she was taking a lesson on November 15, 2018.

It was between 7.30pm and 7.45pm when Sampieri physically assaulted and raped the child in an upstairs toilet of the Arena building.

He locked her in a cubicle and held her at knifepoint, as well as choking her into submission, before assaulting her. Sampieri also filmed the act, according to police, but charges relating to the filming were later dropped.

Nicola Gilio, whose child was at the dance class, went to look for the girl when it was noticed she had been missing for up to 15 minutes. He and dentist Jeffrey Stack, whose dental practice is in the same building, kicked down the door and a scuffle broke out.

Mr Gilio was stabbed in the stomach and the back of his neck with a scalpel during the altercation and the girl’s mother was also slashed on the arm.

Mr Stack, a former amateur boxer, punched Sampieri in the head as he wielded the scalpel, knocking him out.

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Kogarah hairdresser Rachelle Youssef, whose shop is below the studio, told The Leader newspaper that she heard horrible screams.

“I heard this awful screaming like two adults fighting and then this really panicked yelling, ‘call the police, call the police’, over and over,” Ms Youssef told the newspaper.

“It was really terrible. I went outside and the man who was stabbed came out bleeding.

“He was talking on the phone and walking and I said ‘you have to sit down you have blood coming out’. I got Chux superwipes for the bleeding. He sat and then he just laid down in shock. He was overwhelmed.”

St George Police Superintendent Julian Griffiths told reporters after the attack that Sampieri was already in the premises when the girl went to use the bathroom.

“This is a random, serious and concerning scenario where this location has been picked,” he said.

As a result of his guilty pleas today, five charges relating to alleged assaults and using a child to make child abuse material were withdrawn.

In addition to those, the Commonwealth Director of Public Prosecutions withdrew 21 other charges last month. No reason was provided.

After the attack and during court proceedings, it was revealed Sampieri was on parole at the time of the incident but was not wearing a GPS monitor.

And a month before, it was revealed Sampieri was called to a police station to be interviewed over an alleged harassing and menacing phone call he made to a woman.

He was allowed to leave despite a computer search of his name giving a ‘red flag’.

A bearded Sampieri appeared via video link as his lawyer, Penny Musgrave, entered the pleas on his behalf.

He was committed to Downing Centre Local Court for sentence on June 21.