Road workers became visibly ill after exposing suspected radioactive material during a Pacific Highway upgrade on NSW's mid-north coast.
The upgrade's project manager, Bob Higgins, said the workers became sick after unearthing a strange clay-like material near Port Macquarie.
"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 told ABC Radio.
"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."
A truck carrying radioactive waste from Sydney's Lucas Heights nuclear reactor was involved in a crash on that stretch of highway in 1980.
The truck was taking radioactive isotopes to Brisbane so the waste could be shipped to the United Stares. It was subsequently buried near the crash site.
A spokeswoman for the Roads and Maritime Services (RMS) on Wednesday says an exclusion zone has been set up while inspectors confirm the nature of the hazardous material.
"RMS has taken this chemical warning very seriously and the site has stopped work in the affected area," she told AAP.
"Independent chemical specialists are onsite collecting samples for testing. No determination has been made about the potential source of the suspected contamination.
"Tests should be able to confirm if there is a chemical present, what it is and how to remove it so work can restart safely."
The spokeswoman said an area of known contamination was identified earlier during the project development phase. That material was assessed and disposed of off-site.
NSW Greens MP Cate Faehrmann said the presence of radioactive material should have been considered prior to the upgrade, accusing the NSW government of having a "blase attitude".
"It's outrageous that workers and the environment have been put at risk like this," she said in a statement.
"The government knew that highly radioactive waste was there somewhere, but presumably just hoped it would never resurface."
Construction, Forestry, Mining and Energy Union (CFMEU) assistant state secretary Rebel Hanlon said she was concerned about the workers' health.
"We are waiting for the results of the hazardous material inspection," she told AAP.
"We will be closely monitoring the situation to ensure the health and safety of all our members and the community."