SYDNEY- A HOMELESS Australian man was charged on Thursday with rape and murder after four Asian students were subjected to a frenzied sex attack by a knife-wielding intruder in a Sydney apartment.

An 18-year-old Chinese girl was killed and her 19-year-old Korean boyfriend was seriously injured when they fell naked from the third-floor apartment balcony, finally bringing the hour-long ordeal to an end.

Police allege the young couple were repeatedly raped and the boyfriend was forced to indecently assault the girl and two other women, the national AAP news agency reported.

Brendan Dennison, 26, was charged with a total of 21 offences including murder and aggravated sexual assault involving sexual intercourse with the woman and her boyfriend.

He was also charged with using the knife to threaten the two surviving women, aged 19 and 20, with intent to have sex with them, and of robbing one of her Hello Kitty wallet containing 120 dollars.

Police said earlier it appeared the intruder forced his way into the apartment after holding a knife to the throat of one of the women as she was admitted through the building's security entrance.

The dead girl's mother arrived at Sydney airport on Thursday and was picked up by a police escort, the Australian Broadcasting Corporation reported.

A lawyer representing her family told reporters outside the court that the girl's mother lost everything in the Sichuan earthquake earlier this year.

'She lost her business, she lost her home, now she's lost her only child,' Mr Daniel Sheen told ABC.

Dennison, who was arrested on Wednesday night after police released closed circuit television footage showing a man near the apartment building, was remanded in custody and will face court again in December.

The Korean student remains in hospital after suffering serious spinal injuries and multiple broken bones in the fall from the apartment. -- AFP