A BTP statement said: "We continue to work alongside our partners at the scene of a major incident in Croydon.
"We were called at 6.13am this morning after a tram derailed near Sandilands tram stop.The tram's male driver has been arrested in connection with the incident.
"At present, we can confirm five people have sadly died following this incident.
"More than 50 others have been taken to hospital with injuries.
"Officers are continuing to work at the scene and Rail Accident Investigation Bureau are investigating the cause of the derailment.
"One person has been arrested in connection with the incident and is currently in police custody.
"Anyone who is concerned about friends or relatives who might be involved in the incident can call the following number: 0800 056 0154."