The incident was reported on the Northern line just before 6.10pm yesterday (November 17).
Officers say a man was seen with a knife who jumped the barrier and then fled the station.
@oddlytess Today at 6:05pm on the Mordern train from Old Street to Balham – This happened to me at Balham underground tonight. Young guy holding a huge knife/machette ran towards us. Everyone ran and hid on the next tube over. So so scary, glad to be okay. ##london##balham##balhamattack##tube##underground ♬ original sound – OddlyTess
Urgent enquiries are now ongoing to locate the suspect.
A spokesperson for the British Transport Police said: “Urgent enquiries into this incident are ongoing.
“Anyone who witnessed the man or has information is asked to contact British Transport Police by texting 61016 or by calling 0800 40 50 40, quoting reference 511 of 17 November.”
