A 50-year-old man was airlifted to hospital on Friday after falling from a cherry picker at Buildbase in Oxford Road, Calne.
The man, who fell onto a concrete surface from a height of 15ft, was taken to the major trauma centre at Southmead Hospital, Bristol, with serious injuries.
Wiltshire Air Ambulance was called to the scene at 11.27am and the man was also seen by a paramedic from the rapid response crew, and a BASICS doctor.
Police were called to help the air ambulance land safely.
A police spokesperson said the man was unconscious but breathing when the ambulance arrived.
The latest update, given to the police three hours after the incident, was that he remained in a critical condition and had suffered a possible bleed to the brain.
The Health and Safety Executive has not received a report of the incident but the company involved has 14 days in which to do this.