A man was knocked out by a single punch after calling a group of black people 'pets'.
Alarming footage of the incident, which appears to have been shot on the London Underground's Central Line, shows a white man lightly swinging from the handrails.
As he does he shouts 'its my home, all the way back, you know it as well.'
He then shouts incomprehensibly at the men for several seconds.
He then demands that someone out of shot tells him their name before shouting 'no you're black'.
When a woman behind the camera asks what the relevance of the person's blackness is, he tells her to shut up.
The camera angle suddenly switches and the man can be seen rocking back and forward singing 'lesser than us, they're lesser than us'.
The man then yells that the black people on the train are 'pets'.
In a second video that has gone viral online the man, who is wearing a black shirt and light coloured shorts, walks up to a group of black people as they get off the train at Bank Station.
One of them suddenly turns and punches him in the face with a fearsome right hook.
The man falls backwards across the train carriage, completely knocked out.
A woman can be heard laughing as he lies on the floor before shouts break out.
Several seconds later a man rushes to his side, checks his pulse and then puts him in the recovery position.
A female voice off camera says 'don't help a racist.'
It is not clear when the video was taken, although it was uploaded to social media accounts today.
British Transport Police and Transport for London have been contacted for comment.
