Soil that was given to property owners living near the Pacific Highway upgrade works in NSW will be tested after a group of road workers fell sick while unearthing an unknown substance.

During work on the upgrade of the highway near Laurieton, south of Port Macquarie, nearby property owners were given some excess top soil from the site, the Roads and Maritime Services (RMS) said.

The soil will now be tested as a "precautionary measure", RMS said in a statement on Wednesday.

"Arrangements have been made with property owners to establish exclusion zones around the soil until test results become available."

The tests, which will continue today, come after five road workers began vomiting when they dug up an unknown, clay-like substance from the section of the highway just before Easter.

The event initially sparked fears that the workers had hit upon decades-old radioactive material.

It was reported that chemical waste was buried at the site more than 30 years ago after a truck carrying radioactive isotopes from Sydney to Brisbane was involved in a crash.

But so far the soil has tested negative to radioactive material, as well as pesticide, hydrocarbon, biphenyl and other metals.

Nevertheless an exclusion zone that was set up around the area where the workers fell sick remains in place while investigations continue, RMS said.

AAP