A man was attacked with a "corrosive substance" during rush hour at a busy London station.
British Transport Police said they were called to scene following reports of "two passengers fighting" on the platform.
"A man was attacked by someone who threw what is believed to have been a corrosive substance at him," they said in statement, after the incident in the east London suburb of Barking.
"We are in the early stages of the investigation but early indications suggest the victim and offender may have been known to each other."
Witnesses reported the one man threw "something like ammonia" over the other man.
One said on Twitter that staff did not initially intervene, which lead to a train being cancelled after one of the men climbed onboard.
Another witness, Steve Thomas, said on Facebook that he saw the suspect being handcuffed by police while on the train. He said he "only looked to be a teenager".
British Transport Police could not confirm the arrest.
A spokesman for the London Ambulance Service told The Independent: "We sent an ambulance crew and our hazardous area response unit to the scene.
"We checked over a patient at the scene but did not take them to hospital."
The Independent has contacted the rail operator responsible for the station, c2c, for comment.
