The incident happened on the Northern line at Colliers Wood station just before 10.30am today (December 17).
Medics treated a man at the scene for a head injury and he was taken to hospital.
His condition is unknown at this time.
One eyewitness said that two people allegedly “stabbed the f**k out of him”.
He added: “The knife fell onto the track which the police have. The two guys ran away.”
It is also alleged this happened between the platform and the train, with the victim on the carriage and the other two next to the doors.
“People were really shook up,” he added, “It was brutal, absolutely brutal.”
These claims have not been verified at this time, although we are working to get confirmation from police.
There were initially severe delays across the Northern line due to the incident.
At the time of reporting, there are now minor delays between Kennington and Camden Town via Bank, northbound only.
Colliers Wood station remains closed as police investigate.
A London Ambulance Service spokesperson said: “We were called at 10.29am today (17 December) to reports of a stabbing at Colliers Wood Underground Station, SW19.
“We sent resources to the scene including an ambulance crew, an incident response officer and a paramedic in a fast response car.
“We treated a man for a head injury and took him to hospital.”
