A man is in custody after he allegedly impersonated a police officer and detained and raped a woman in Sydney's south-west on Friday morning.

Luke Snowden faced nine charges at Parramatta Bail Court on Saturday, including a host of sexual assault and theft charges over incidents in the early hours of Friday at Minto.

Police allege the 23-year-old contacted two adult services agencies in the Minto area on Friday, telling two women he was a police officer.

He allegedly sexually assaulted a 45-year-old woman about 2am, after they met on Hansens Road in Minto.

After the alleged incident, the woman and her driver visited the nearest house and alerted the residents, who contacted police, before she was taken to Liverpool Hospital.