Emergency services have been called to Clapham Junction station after a person fell between a train and the platform.
Trains may be cancelled or delayed by up to 30 minutes after the incident, which is believed have happened on Platform 12.
Southern Rail confirmed the passenger had been injured on one of the northbound lines which they use at the station, which is Britain’s busiest.
A British Transport Police spokesman said: “We were called at 12.28pm to reports of a casualty on the tracks.
“A person had fallen between a train and the platform. We remain on the scene.”
A London Ambulance Service spokesperson said: "We were called at 12:07pm today (11 June) to reports of a person injured at Clapham Junction station, Clapham.
"We sent a medic in a response car and an ambulance crew to the scene. We treated a person at the scene and took them to hospital."
Disruption is expected until 2pm.
