A shipment of spent nuclear fuel rods from the Lucas Heights nuclear reactor has left Port Kembla on the New South Wales south coast bound for the United States.

The Australian Nuclear Science and Technology Organisation (ANSTO) advised the public in November last year it was planning to ship radioactive spent nuclear fuel to the US in sealed casks.

ANSTO will not confirm if the shipment occurred early this morning, but the ABC has been told eight containers escorted by three busloads of police arrived at Port Kembla to be loaded onto a ship at 1:30 am AEDT.

The ship left port at 4:30am escorted by a police boat and helicopter.

Police media has confirmed police worked with ANSTO on a security operation overnight, but will not elaborate.

New South Wales Greens MP Lee Rhiannon says dangerous road conditions in the Illawarra make it unsuitable for transporting nuclear waste and residents should have been warned.

"The area of the Illawarra has many notorious blackspots, there's been many truck accidents and the Greens remain concerned about how this operation was conducted and that such high level nuclear waste was taken from Lucas Heights down the escarpment to Port Kembla," she said.