A construction worker has been killed after being hit by the scoop bucket of a truck.

He was standing near the tip truck at a demolition site at Airds in Sydney's south-west. The truck was being loaded by an excavator when its scoop bucket came loose and fell on top of him.

According to police, the man suffered serious head and chest injuries and died at the scene.

He has not been formally identified.

Police secured a crime scene and the incident will be examined by detectives and WorkCover investigators.