Officers are appealing for information after a teenager was shot at Barking train station late on Wednesday evening.
Just after 11.30pm BTP officers, along with colleagues from the Metropolitan Police Service, were called to a report of a man having being stabbed at Barking train station.
The London Ambulance Service took the victim to hospital, where a small bullet was discovered inside his abdomen. He remains in a serious condition.
It is believed there was an argument which took place on board a Hammersmith and City train between the victim and the two suspects which then moved onto the platform. Following the incident the two suspects fled the station on foot. No arrests have been made at present.
DCI Sam Blackburn from British Transport Police, said: “This was a violent and rare attack which took place on a late night train out of London. Officers were on scene within minutes and we are working hard to identify and trace the men responsible for this assault.
“We understand that this was a frightening incident for passengers on the train and at the station, and would encourage anyone who witnessed the attack or the moments leading up to it to come forward and tell us what they saw.”
The incident is not being treated as terror related.
Police are asking that anyone who was at Barking train station and saw anything suspicious, to please get in touch.
Anyone who witnessed the incident or with information should contact BTP by sending a text to 61016, or by calling 0800 40 50 40 - quoting reference 685 of 20/02/19.
Alternatively you can call Crimestoppers anonymously on 0800 555 111.