A man has been killed in what appears to be a horrific tragedy at a children's playground on the central coast.

Contractors at Copacabana were using a sand-blowing truck to fill the playground at Shaun Brinklow Park with sand on Wednesday when the machine suddenly seized. The workers went to investigate what went wrong and they found a man dead in the back of the truck with traumatic injuries.

Police look into the back of the sand-blowing truck, where the man's body was found. Credit:Justin Wilson

Several witnesses had seen the man approach the contractors a short time earlier and a brief conversation took place.

The semi-trailer bore signage for The Hills Bark Blower and has a steel ladder at the back that allows access to the trailer.