The London Ambulance Service was called to Walworth Road, near Elephant Park in Elephant and Castle.
Paramedics arrived in less than seven minutes but a person died at the scene.
Police cordoned off an area of the road near the junction with Deacon Street shortly afterwards.
A London Ambulance Service spokesperson said: “We were called at 7.57pm yesterday (8 December) to reports of an unwell person in Walworth Road, SE17.
“We sent ambulance crews, an advanced paramedic and an incident response officer to the scene.
“The first paramedic arrived in less than seven minutes.
“Despite the efforts of the crews, a person sadly died at the scene.”
