Police were called to Stratford DLR station around 4.20pm yesterday (August 23).
As officers approached the man, he allegedly went onto the tracks.
Officers then worked with station staff, paramedic and the London Fire Brigade to bring him back to safety.
The man was taken to hospital and later arrested on suspicion of trespass, endangering the railway and a public order offence before being taken into custody.
Police did not say if a firearm was recovered.
The station was closed and the DLR was suspended between Stratford High Street and Stratford International “while the police respond to an incident at Stratford”, according to TfL.
A BTP spokesperson said: “Officers were called to Stratford DLR station at around 4.20pm yesterday (23 August) after a man told station staff that he had a firearm.
“When officers approached the man he entered the tracks.
“Officers worked with staff, paramedics and the London Fire Brigade to bring the incident to a safe conclusion.
“The man was taken to hospital as a precaution and later arrested on suspicion of trespass, endangering the railway and a public order offence before being taken into custody.”
