Kathu Police were notified of the accident at 2:20pm. Officers arrived at the scene, opposite the Kathu Social Security Office on Phra Phuket Kaew Rd in Moo 4, Kathu, to find a six-wheeled private garbage truck parked on the roadside.
The victim, identified as Myanmar national Wai Lin Kyaw, 28, had already been taken to hospital after suffering severe injuries in the fall.
The truck driver, Anuthai Jindahtam, 23, told officers that he and two workers had been transporting garbage bags to sell at a recycling shop. Mr Wai Lin and another worker had been sitting on one of the bags in the back of the truck when it suddenly shifted and fell off the vehicle.
Mr Wai Lin reportedly fell about 3.8 metres onto the road, suffering serious head injuries and losing consciousness.
Rescue workers from Kathu Municipality and volunteers from the Kusoldharm Phuket Foundation performed CPR at the scene before an ambulance from Bangkok Siriroj Hospital transported Mr Wai Lin to hospital, where he was later pronounced dead.
Police have recorded the incident and sent the body to Vachira Phuket Hospital for a post-mortem examination and further legal proceedings.
Officers reminded workers to take care when travelling on open trucks and avoid sitting on unsecured loads, especially when the vehicle is in motion.
Police made no mention of any charges for the incident.