Smoke was seen coming from the carriage as the train pulled into Leyton Underground station around 10.13pm on Saturday, police have said. Officers were called to the scene just before 11.50pm to reports of a bag on fire.
Footage captured at the scene shows how the carriage was filled with foggy, grey smoke as the bag burned on the floor. Travellers stood along the platform watching and taking pictures and video as the blaze continued.
It is unclear how many people were aboard the train when the fire broke out or at what point the carriage was evacuated.
But footage of the aftermath shows how the interior of the carriage was burnt and left covered in black soot.
The floor where the bag had been placed was completely melted and at least one glass window pane was shattered.
Detectives are asking anyone with information or footage of the incident and any witnesses.
Investigators are particularly interested to speak those who were travelling on the train.
Eyewitness are being asked to contact British Transport Police at on 0800 40 50 40, or by texting 61016 with the reference 747-021223.