Rescue workers took almost four hours to free the man's mangled body, as horrified colleagues looked on.

The incident happened at about 7.45am. The cause of the derailment has not yet been confirmed but police said preliminary investigations showed one of the tracks was broken.

Spoornet corporate communications manager Joseph Strutt said the freight train was carrying oranges from Patensie and was about to off-load the cargo at the pre-cooling shed when the incident occurred.

"It was a normal shunting movement and the train was moving slowly on the narrow gauge. We do not know what caused the locomotive to derail," Strutt said.

Three goods containers being pulled by the locomotive also left the tracks, with the one behind the engine overturning and smashing into the officer who was standing behind the locomotive to re-route it towards its destination.

Police identified the dead man as Mthuthuzeli Adams, 48, from New Brighton, who was employed by Spoornet as a yard official.

Police spokesman Thembi Gwe said the results of a preliminary investigation revealed that one of the tracks was broken. "The train was changing lanes and the man was trapped in between the engine and a container. It was not moving at high speed," Gwe said.

At the scene of the accident, opposite the second security gate to the pre-cooling shed, a concrete lamp pole was flattened and a portion of the palisade fence next to the gate was ripped apart.

Movements of freight trains in and out of the harbour were suspended for the day. Dozens of shocked Spoornet workers watched as the body of their colleague was removed.

One of the workers who witnessed the accident said he heard the official crying for help but nothing could be done to help him. "This thing was so sudden. No one expected it. I never thought anything like that could ever happen. I still cannot believe it," he said.

Police, ambulance and emergency services, including a Spoornet technical team, were immediately called to the scene from the harbour control room.

The wreckage was only cleared yesterday afternoon following the careful extrication of Adams's body. The technical team also had to firmly anchor the first goods container so it did not topple further.

A labour department inspector was called in to investigate whether safety measures were adhered to by the parastatal. "This is the worst accident in years," Strutt said.

"Accidents like these are not a common occurrence because we stick to safety standards."

He said Spoornet management had visited the Adams family yesterday to convey their condolences and had undertaken to assist with anything they could to ease the family's trauma.

He said the company would also launch its own investigation.