The woman in her 50s, who lives with disabilities, was in a mobility scooter on the platform at Ormond train station just before 10am when it is believed she accidently fell onto the tracks, just before a train came through the station.
Acting Senior Sergeant Rowan Epstein has said police believed the woman had gone too close to the edge of the platform, and had fallen out of her scooter.
He said the woman is believed to have fallen less than a minute before an outbound train, which wasn’t stopping at the station, passed through.
Epstein said there were other people on the platform at the time, but no one reported seeing the woman fall.
The train driver alerted police before paramedics arrived and rushed the woman to the Alfred Hospital in a critical condition.
Police are investigating the circumstances surrounding the incident and how she came to be on the tracks.
Anyone who witnessed the incident and who hasn’t spoken with police is urged to contact police.
Trains on the Frankston line have been replaced with buses between Caulfield and Moorabbin stations.