Australian police said on Wednesday that the four occupants of a Sydney unit were forced to strip naked and sexually assaulted by a knife-wielding intruder, before two teenagers fell from the balcony, and one died.

Liao Wei, 18, died after falling from her third-floor unit early Sunday afternoon. Her South Korean boyfriend Tae Wook Han, 19, suffered two broken legs, a fractured pelvis and fractured vertebrae in the fall and remains in hospital facing possible permanent damage.

Investigators have seized CCTV footage of the intruder, a man aged in his mid-20s who forced his way into the Waterloo unit, and plan to release his image later Wednesday. He is described as about 175cm tall with a strong, dark complexion, short dark hair and was last seen wearing shorts, a T-shirt and running shoes.

Detective Superintendent Geoff Beresford said that police had interviewed Han in hospital and his information had been "very helpful".

He said all the four occupants of the unit - three Chinese female students and Han - had been sexually assaulted. The other two Chinese women were escaped unharmed.

"We can confirm that there were a number of sexual assaults on all of the victims," Australian Associated Press quoted Beresford as saying in Sydney.

"In relation to the deceased person and obviously the male person who suffered injuries from falling, we do expect that they were forced either by force or by other means (off the balcony)," he said.

(Xinhua News Agency October 29, 2008)