A casualty on the tracks was reported on the Southeastern line at around 9.40am yesterday (September 16).
Officers and London Ambulance Service crews attended and a woman was rushed to hospital for treatment.
Her condition was initially unknown.
A spokesperson for British Transport Police confirmed today (September 17) that her condition was assessed as life-changing.
The incident is not being treated as suspicious.
Lines between Lewisham and Barnehurst are closed as the incident is being dealt with.
All services have since returned back to normal.
A spokesperson for London Ambulance Service said: “We were called at 9.42am today (16 September) to reports of a person hit by a train at Welling Rail Station, Welling.
“We sent resources to the scene, including an ambulance crew, a paramedic in a fast response car, an incident response officer and paramedics from our hazardous area response team (HART).
“We also dispatched a trauma team in a car from London’s Air Ambulance.
“We treated a woman and took her to a major trauma centre by road as a priority.”
A spokesperson for British Transport Police said: “Officers were called to Welling railway station at around 9.40am today (16 September) following reports of a casualty on the tracks.
“Paramedics also attended, and a person has been taken to hospital with injuries that are still being assessed.
“The incident is not being treated as suspicious.”
If you’ve been affected by what happened on the network today, there is always someone to talk to.
You can contact the Samaritans on 116 123 from any phone for a confidential chat.