A joint police investigation is underway after a 17-year-old girl from West Africa escaped a Sydney house where she was reportedly held as a sex slave.

Police said the teenager, a Guinea national, was “in fear for her life” as she fled in the early hours of April 27 and ran until she was picked up by a woman who took her to the Asylum Seeker Centre in Newtown, in Sydney’s inner west.

She had allegedly been held captive in a room in the house for several weeks and had been regularly sexually assaulted by a number of men, police said.

Police are appealing for the woman who helped her – described as a “Good Samaritan” named “Nicole” who drove a small red car – to make contact with police.

After consultation with Sydney’s University of Technology anti-slavery unit, the girl was taken to the Royal Prince Alfred Hospital for treatment and later placed into the care of the NSW Department of Family and Community Services.

The Australian Federal Police and the NSW Police Force were contacted and commenced investigations into the circumstances surrounding the girl’s arrival into Australia and the reported incidents since that time, including sexual assaults.

NSW Police Acting Superintendent Mick Haddow told reporters on Friday it had been a very difficult investigation and they were continuing to piece together her movements, where she was held and whether she had any relatives in Australia.

“She believes she arrived in Australia in early April so we’re looking at a period of weeks.

“This girl has escaped from a unit, she’s waving for attention from the public, and she’s managed to be collected by this person we know as Nicole so one can only imagine that she was upset.

“She is being looked after the best she can be.

“It’s a very traumatic situation,” he said.

The girl told investigators she met a man in her home country, Guinea, in January who offered to bring her to Australia to work as his cleaner.

In early April, the girl travelled with him from Guinea to Sydney, flying via Paris, which took a number of days. He then drove her to a house in suburban Sydney where she was held captive.

“We are really seeking help from this person, known as Nicole, who in the early hours of the morning collected this young girl and took her to the Asylum Seekers Centre,” Detective Haddow said.

“She is a really important witness, Nicole, and also potentially a really important source of information for us in terms of identifying the crime scene,” he said.

The AFP’s human trafficking unit has been brought in to investigate when the girl arrived in Australia, along with NSW Police State Crime Command’s sex crimes squad under Strike Force Stockall.

AFP Commander Chris Sheehan said how the teenager arrived in Australia, the passport she travelled under and who she travelled with were “critical” lines of enquiry.