The materials, which include caesium, were buried north of Port Macquarie after a road accident in 1980.

 

In that incident, a truck carrying radioactive isotopes from Sydney's Lucas Heights nuclear reactor crashed.

 

The material was being taken to Brisbane on its way to being shipped to the United States.

 

The upgrade's project manager, Bob Higgins, says road workers fell ill after unearthing a strange material.

 

"As we've taken down the cutting there we exposed the face of the existing material (and) came across a clay material that when it's exposed to air it gets an orange streak through it," he said.

 

"There were a number of workers that felt a little bit of nausea and there was a bit of vomiting when they were in close proximity.

 

"(They went) off to the doctor, but obviously we need to be extremely careful here."

 

The Environmental Impact Statement for the highway upgrade had noted some uncertainty about where exactly the containers were buried.

 

Specialists are in the area assessing what to do with the radioactive materials, and if they pose any risk.