A Tube passenger filmed the moment a Jubilee line train travelled at full speed with several doors wide open.
Video of the incident shows the Saturday morning service travelling between Finchley Road and West Hampstead station with the doors wide open.
Transport for London (TfL) said the incident is being investigated.
Responding to his post, Transport for London (TfL) said: "We are aware of this incident and when this happened, the train was then taken out of service.
"Customers safety is our top priority, and we are investigating this to ensure it doesn't happen again."