He said the woman struck out at the man's head and face and screamed.
Mr Smith said the man ran towards Te Ngae Rd and turned right towards the Owhata shops.
"It's been a frightening experience for this woman and we'd like to identify this attacker as quickly as we can to spare anyone else the trauma of a similar assault."
Meanwhile a self defence organisation has praised the woman's efforts.
The Women's Self Defence Network Wahine Toa, which teaches self defence to women across the country, said it was impressed by the woman's courage.
"She obviously fought back with considerable effectiveness so that the assault ended with the attacker running off," said spokeswoman Alison Broad.
"It is always disturbing to hear of any attacks on girls and women, but it is great when an attack is so effectively thwarted.
"Our congratulations to the woman concerned. It seems she put into practice the key responses we would recommend for any woman or girl who is attacked."
The offender is described as a male Maori aged in his mid to late teens. He is of skinny build with a long thin face and no facial hair. He is likely to have a scratch or injury to his face as a result of the victim fighting back.
He was wearing dark clothing, including a hooded sweatshirt and denim jeans. He smelt of alcohol.
Anyone with information is asked to contact Rotorua police on (07) 348 0099. Information can also be provided anonymously to the organisation Crimestoppers on 0800 555111.
