A woman has been arrested after an online video apparently showed a woman abusing ethnic minority passengers on a packed south London tram.
The clip, viewed more than two million times since being uploaded to YouTube on Sunday, shows a woman sitting with a child, shouting at fellow passengers.
British Transport Police said a woman, 34, had been arrested on suspicion of a racially-aggravated offence.
The incident happened on the Croydon to Wimbledon Tramlink route.
Police are yet to clarify exactly where or when the incident happened.
In the online clip, the woman confronts several passengers, saying: "You are not British". She then starts swearing.
When one passenger asks her to mind her language, saying "there are little kids on the tram", the woman points to the child on her lap and says "I've got a little kid here".
The woman then says: "Go back to where you come from".
'Not entirely clear'
In the video she then starts shouting at the woman who asked her not to swear, before another passenger intervenes, saying: "I am English, what have you got to say to me?"
A British Transport Police spokesman said: "The video posted on YouTube and Twitter has been brought to our attention and our officers have launched an investigation.
"At present it is not entirely clear which tram stops the offence took place between and when it occurred.
"As a result, we need anyone who witnessed this incident, or with any information that could assist our investigation - including the identity of the woman - to contact us.
"We will not tolerate racism in any form on the rail network and will do everything in our power to locate the person responsible."