The stray cat culling was performed by a licensed contractor ordered by Port of Newcastle.

The port said it acknowledged the incident was "unacceptable".

"The outcome is distressing for everyone and does not meet our expectations nor align with our values as an organisation," Port of Newcastle said in a statement.

"We have launched an urgent investigation into this unacceptable incident.

"PON has engaged an expert to urgently look for any other injured animals and get them assessed."

But the port stood by its decision to cull the stray animals, saying it was done so "in response to growing risks to the community and the environment".

Rochelle Wood, who is the founder of the Stray Cats Project that catches, desexes, microchips and rehomes stray cats on the breakwall, said she was horrified.

"If they had any sort of community mindedness they would have contacted us instead," she said.

"What sort of health and safety issue could there be from cats that have been desexed and fed everyday? What sort of harm could they do?"

The group has managed to reduce the number of stray cats on the break wall from 100 to about 40 through desexing and re-homing over the past few years.

Ms Wood said the first they heard of the culling was when feeders turned up on Friday morning and found "blood and fur everywhere". They called the police, initially believing it was a citizen who had hurt the animals.

"There were trails of blood to the rocks, where they must have gone to hide," she said.

"One cat was really injured, she had a bullet go through her skull so she's now blind for life, and had bullet wounds to the lower part of her body. She's not well but we'll try and save her."

Volunteer Di Weaver managed to capture the blind cat after following a trail of blood. She said the situation had left her "heartbroken and devastated".

Ms Wood said the vet informed her that the port had offered to pay the cat's vet bill, but she said that "meant nothing".

She said removing desexed cats from an area would lead to non-desexed cats claiming the territory.

"You'll never kill them all, they will breed, breed, breed," she said.

The group went back out on the weekend to try and find and help the animals that survived.

"I'm worried about the ones that are out there still suffering," Ms Wood said.

"We'll never know how many animals were shot.

"The feeders this morning were just in tears, they've bonded closely to those animals. They're really like an extended pet, they're all microchipped. It's really sad."

Animal Justice Party MP Emma Hurst is calling on the authorities to urgently investigate the matter.

"This sounds like a horrendous bloodbath and it's simply not enough that the Port of Newcastle is conducting their own internal investigation," she said.

"The authorities must step in and investigate possible breaches to our animal protection laws."