A woman who rushed to board a London Overground train was dragged 20 metres along a station platform after her hand got trapped in the train door.
The commuter tried to board a train as it was about to leave Wood Street station in Walthamstow at 8:22am on 14 January, the Rail Accident Investigation Branch (RAIB) said.
The doors closed with the passenger's hand trapped inside the rear doors of the fourth car and she was forced to run alongside the service.
It travelled for around 20 metres along the platform before stopping and opening the doors.
The passenger did not sustain any injuries, the branch said.
The RAIB said it has undertaken a preliminary examination into the incident and will publish a safety digest.
Rory O’Neill, TfL’s General Manager for London Overground, told ITV News London: "We're sorry that our customer experienced this incident, which must have been extremely upsetting for them.
"While thankfully there were no physical injuries in this rare incident, we're committed to running the safest network possible and a thorough investigation is underway to help prevent this happening again."
Arriva Rail London, who operate the London Overground on TfL’s behalf, is undertaking a full investigation and fully co-operating with the RAIB.