Police were called at around 3pm to a bus and train station in West Croydon. A large police cordon has been placed in surrounding areas and some buildings have been evacuated.
Road closures are in place and transport services have been disrupted.
Specialist officers from the Met Police are leading the investigation.
In a statement, Croydon Metropolitan Police Service said: “Cordons are in place near West Croydon BR Station after officers became aware of a suspicious vehicle at around 15:00hrs.
“Specialist officers are attending to assess. Some buildings/ shops evacuated as a precaution.
“Road closures are in place. Motorists should use alternative routes. Bus & train services have also been disrupted.”
This is a developing news story, more to follow.