Firefighters and officers were called to attend a passenger train that partially derailed on the overground section of track near Wimbledon train station.
A rear carriage derailed at a slow speed and while there were around 300 people on board, four people were reported to have minor injuries.
Station Manager Cathi Reeve who is at the scene said:
"Our specialist Urban Search and Rescue teams quickly helped passengers from the train and thankfully there were only a few minor injuries."
Crews from stations including Wimbledon, New Malden and Mitcham fire stations were at the scene.
The Brigade was called at 0559 and the incident was over by 0909.