A Toronto doctor is facing sexual assault and other charges for allegedly paying to have unprotected sex with a 15-year-old and then injecting her with birth control medication after every encounter.

Police said they have charged Ernest Chiu, 32, with sexual interference, invitation to sexual touching, obtaining sexual services from a person under 18 and sexual assault.

The accused reportedly had sex with the minor girl at different hotels in the city and once at his office at Toronto General Hospital. He came in the girl's contact after he responded to a newspaper advert for an escort service, police said.

"Members of our human trafficking enforcement team began an investigation into the trafficking of a 15-year-old girl. During that investigation they became aware of this man and further investigated his involvement," Toronto police spokesperson Meaghan Gray told CBC Toronto.

"We are alleging that he procured sex from her knowing that she was 15," Gray added.

Investigators are currently probing the alleged trafficking of the girl, whom the doctor first met in December 2016, according to the Toronto Star. They said that Chiu is a Nephrologist and is associated with multiple health organisations in the city, including St. Michael's Hospital, Toronto General Hospital, Toronto Western Hospital, Princess Margaret Hospital, Toronto Rehab and Sinai Health System.

Chiu studied medicine at the University of Toronto and was issued a speciality in Internal Medicine on 8 May. His post-graduate study in nephrology completed in June, according to the College of Physicians and Surgeons of Ontario's records.

However, the College's site, as of Thursday (12 October) afternoon, showed that his medical license expired in June.

"We are shocked by the allegations, which are inconsistent with our values and our expectations that everyone who works at St. Michael's, including trainees, adheres to the highest possible standards of behaviour in both their personal and professional lives," the hospital told CBC Toronto in an email statement. It added that they were cooperating with the ongoing investigation.