A dog came to the rescue of its owner, biting an armed man who was attacking her.
The 19-year-old woman was in a Christchurch park with her dog just before 2am today when she was attacked, Detective Greg Dalziel said.
The woman fought back, and so did her dog.
The woman suffered cuts and bruises when she was jumped by the man who police said had a weapon on him in Jellie Park, Burnside.
But she scratched her attacker and her dog bit the man in the shoulder or neck, Mr Dalziel said.
"The injuries are likely to be causing the offender discomfort,'' he said.
In another, unrelated incident, a 14-year-old girl was attacked and pulled into bushes in the central city about 9.30pm on Friday.
She suffered bruising but no other serious injuries, Mr Dalziel said.