The incident was reported near the railway in the Wimbledon area just before 2.30pm today (December 8).
All lines have since closed, causing cancellations and delays to South Western and Thameslink services.
Major disruption is expected until the end of the day.
No trains will run between Streatham and Sutton through Wimbledon until further notice.
The nature of the incident is unclear at this stage.
A South Western Railway spokesperson said: “Response teams are on their way to site. In order to allow emergency services access to the railway all power to the track will need to be switched off in the affected area.”
“At this time, we estimate that disruption to our services will end at the end of the day. All lines are blocked and your journey is likely to take longer.
“We will let you know if this changes or when we have more information.”
We have contacted British Transport Police and London Ambulance Service for further details.
This is a breaking news story. More to follow.
