There is a renewed push for the Ulladulla Harbour on the New South Wales south coast to be heritage-listed, after a fossil was cut from rocks using an angle grinder.

Volunteers from the Gondwana Fossil Walks group noticed the 270-million-year-old fossil missing earlier in January.

Group president Phil Smart said he was baffled as to why someone would want to take the fossil.

"I was startled to see that someone with an angle grinder had been active again," Mr Smart said.

"This happened three years ago. A little square was cut out of the rock platform to remove a single fossil.

"This time, a similar-sized square, which has all of the hallmarks of the same operator, has been used to remove another fossil."

Mr Smart said the fossils were of little monetary value, but were significant in documenting biodiversity in the harbour over millions of years.

"We're not actually sure which fossil went the second time, but the one that was taken the first time, we're very familiar with it," he said.

"It was a pecten shell, of low quality. The resolution, the sharpness of the features was poor.

"It would fetch no more than $5 or so on eBay, if someone chose to sell it.

"The untouched Ulladulla platforms have real heritage status. The heritage value here is both educational and scientific."

Group needs help with heritage listing application

Gondwana Fossil Walks has applied for the area to be added to the National Heritage List.

The original proposal included a written letter of support from Dr Bruce Runnegar, director of NASA's Astrobiology Institute and professor in the University of California, Los Angeles' Department of Earth and Space Sciences and the Institute of Geophysics and Planetary Physics.

"It wasn't rejected, our application, it was certainly looked at seriously and the panel said, 'We want more information about significant research that's been done on the rock platforms'," Mr Smart said.

The damage left on the rock platform at the Ulladulla Harbour where a single fossil was removed using an angle grinder. ( ABC Illawarra: Ainslie Drewitt-Smith )

"As a group of volunteers, we simply haven't had the time.

"We will ultimately get around to it. It would be nice if we got some support from someone from a university or somewhere, to give us a bit of help on that."

Ulladulla's Fossil House volunteer and manager Julian Sharrad believed having the area heritage-listed would provide greater protection against vandals.

"It would give better recognition that this is a significant site to come and have a look at," Mr Sharrad said.

"It would give us some protection from the people who would come and cut pieces out of the rock platform if there is a particularly nice specimen, and they want to keep it for themselves rather than leaving it for the tourists and everybody else, and other scientists who would come and study these rocks."

Anyone with information about theft of the fossil is being urged to contact the police, but Mr Smart said he would be happy to teach the culprit a lesson.

"Please come and see us. If you're really keen to add to your collection, or you're so desperate that you need a few fossils that you can sell, come and see me at the fossil house," Mr Smart said.

"I do have material that is spare, that is better than what you've picked up out of the rock platform, and I'd be happy to give it to you."