An elderly man was repeatedly punched on a London underground train and apparently knocked out of by the force of it, this shocking video shows.

(Viewer discretion is advised)

The video shows the man and another passenger arguing and struggling with one another. The other man then stands up and attacks him, apparently kneeing him in the face after punching him.

British Transport Police detectives have released an image of a man they they want to speak to in relation to the incident, which took place at Aldgate East London Underground station on Monday.

Detective Constable Lawrence Murphy, who is leading the investigation, said: “At 9.20pm onboard a District line train, a physical altercation occurred between two men which resulted in a fight which left a man requiring hospital treatment.”

-Huffington Post