She was grabbed by a man and pulled into an alleyway this morning.
The victim, who's in her twenties, was walking along Wallingford Street at around 12:15am.
She managed to escape her attacker and raise the alarm with a passing vehcile.
The offender is described as a mixed race man in his twenties, with curly black/brown hair, and was wearing dark clothing.
Senior investigating officer, Detective Inspector Steve Raffield, of Force CID, said: "This is a concerning incident and we are carrying out a thorough investigation and following a number of lines of enquiry to gather further information.
“We are asking members of the public who were in the area of Wallingford Street at around 12.15am this morning to come forward and please call 101 quoting reference 12 of 11/06/18.
"As a result of this incident members of the public may see an increased police presence and patrols whilst we continue to investigate."
The victim is being supported by specially trained officers.