The operator had been bogging out the face when the front right wheel of the vehicle dropped into a hole in the floor.
He immediately exited the LHD and advised the mine supervisor.
The area was barricaded off for safety.
The following morning an inspection of the scene found a void had formed and the LHD had dropped to the level below.
The NSW Resources Regulator said mine operators must continually assess and monitor known voids to ensure they are adequately mapped, and separation distances are maintained.
The incident is being further investigated by authorities.