After arriving at the scene shortly after 10am, officers found a woman with a stab wound to her neck.
The woman, aged in her 40s, was taken to hospital with non-life threatening injuries.
A statement from the police said: “Police were called at 10.10am on Wednesday, September 21, to reports of a stabbing outside Gants Hill Underground Station. Officers attended along with the London Ambulance Service.
“A woman, aged in her 40s, was found with a stab wound to the neck. She has been taken to hospital and her condition is not life-threatening.
“Enquiries are ongoing to establish the circumstances of the incident.”
No arrests have been made at this time.
Any witnesses or anyone with information about what happened is asked to call 101 quoting CAD 2064/21Sep.
To remain anonymous, contact the independent charity Crimestoppers on 0800 555 111.