Two people believed to be an adult and a child have died after being hit by a rush hour train at Ealing Broadway station on 23 June after falling on the tracks just after 6pm.
IBTimes UK confirmed a First Great Western train on the 15.55 Cardiff to Paddington service was involved.
Speaking to the BBC, British Transport Police said: "We were called at 6.10pm to Ealing Broadway station following reports that someone had been hit by a train. We attended along with the Metropolitan Police, London Ambulance Service and London Fire Brigade and discovered two people had been struck and killed by the train. We're still working to determine the identities of the deceased or how they came to actually be on the tracks."
One commuter told the Evening Standard: "I'd just got off the Central line. As I looked over to see how many people were standing on the [opposite] platform I saw the train going round the other side of the platform and I heard the horn. I saw everyone reacting and I just knew. People were just shocked. I could see everyone's faces, and I knew straight away. TfL came downstairs and started evacuating [the platform]."
Others described the scene as a "nightmare", with police, ambulances and fire engines congregating around the station.
A British Transport Police spokesman said: "Officers are working to determine the identity of the deceased and to establish how they came to be on the tracks. Clearly the investigation is in a very early stage and, at present, the incident is being treated as unexplained."
London Ambulance Service said staff including its hazardous area response team had been sent to the station but that two people had been pronounced dead at the scene.
Correction: An earlier version of this story incorrectly stated a Heathrow Express train was involved in this incident. This has now been amended.