Lower Hutt police are investigating a serious assault with "suspected sexual overtones" near the Ava rail bridge on Wednesday night.
Detective Senior Sergeant Paul Borrell said the 25-year-old woman was approached by a man, who grabbed her hair, about 5.30pm.
"The offender was armed with a knife, however, the victim screamed and was able to get free of the offender, and he then ran through Memorial Park towards Wilford Primary School."
Mr Borrell said police have spoken to a number of witnesses since the incident.
"This critical information has assisted us hugely in locating several articles including a hooded sweatshirt. We are still searching for a pink cell phone thought to be discarded by this man in the vicinity of the Ava rail bridge."