Firefighters were called to assist emergency services at a serious collision at a school on Camp Road in Wimbledon.
Deputy Assistant Commissioner Andy Pennick said: "This is an incredibly sad incident and our thoughts are with the family, friends and the local community at this difficult time.
“On arrival, our crews provided safe access for emergency services to the incident scene by removing safety railings using specialist equipment. Firefighters also assisted London Ambulance Service crews with providing immediate emergency care to members of the public.
"We are now engaging with the community and providing support as needed.
“The welfare of our staff involved in this incident is very important to us and we have set up a wellbeing centre at a local fire station. All staff will be offered counselling as a priority."
The Brigade was called at 1018 and the incident was over for firefighters by 1250. Two fire engines and two fire rescue units attended the scene.