A man has been rushed to hospital with a chest injury after falling through the ceiling of a disused factory.
London Ambulance were called to Stewart House in Waddon Marsh Way, Waddon, just before 8.40am to reports of a fall from a height.
A spokeswoman for London Ambulance confirmed they sent an ambulance crew, a single responder in a car, a duty officer and the medical team from London's Air Ambulance in a car.
Staff treated a 56-year-old man who is understood to be a construction worker, at the scene, before he was taken as a priority to St George's Hospital in Tooting.
Police have cordoned off the factory and the Health and Safety Executive (HSE) confirmed they had sent inspectors to the scene.
A spokesman for the HSE said: "We are aware of the incident and are making initial enquiries."
A drilling company employee that arrived to work on a neighbouring site shortly after the man fell said: "He must have fallen a few minutes before we got there.
"Two security guards came over and asked if anyone knew first aid. I do so I went to get the kit out of the van but then an ambulance arrived so I wasn't needed.
He added: "I saw the man being taken away with his head bandaged up. He was conscious."
Plastics company Stewart occupied the factory until last year when they moved to Banbury, in Oxfordshire.