The fight between two men involving a knife at Willesden Junction station happened at 7.48pm yesterday (January 13).
Officers and London Ambulance Service crews attended and treated a man who had injuries that were not thought to be life-changing or life-threatening.
It is understood that the man was not stabbed but instead he was cut from the weapon.
The Mildmay Overground line was suspended due to the incident, with no trains between Willesden Junction and Richmond or Clapham Junction.
There were severe delays across the rest of the line.
A British Transport Police spokesperson said: “Officers were called to Willesden Junction at 7.48pm yesterday (13 January) following reports of a fight between two men at Willesden Junction Underground station involving a knife.
“Paramedics also attended, and a man was found with injuries that were not thought to be life-changing or life-threatening.”
An investigation is ongoing and anyone who witnessed incident should contact the British Transport Police by texting 61016 or by calling 0800 40 50 40, quoting reference 295 of 13 January.
