The incident happened in Firth Road near Tamworth Road at around 9am yesterday (May 31).
Officers and London Ambulance Service crews attended and two people found injured.
The woman, who is in her 20s, died at the scene, despite the efforts of a teenage boy to help her, police said.
A man in his 30s was taken to hospital with minor injuries.
He was later arrested on suspicion of murder and remains in hospital.
Initial inquiries by the Met suggest the incident started at a nearby address, before escalating onto Frith Road.
Superintendent Mitch Carr said: “This is a tragic incident where a young woman has lost her life and our thoughts are with her loved ones.
“I especially want to thank the members of the public, including a teenage boy, who bravely tried to help the victim.
“We believe that this was an isolated incident, but understand that this news will shock the local community.
“Officers will remain in the area over the coming days and we would ask anyone who has concerns to speak with them.”
