The invasive and poisonous pest was discovered by a resident sitting by a dam on a Somersby farm on Tuesday.

The family captured and brought it to the nearby Australian Reptile Park.

The discovery has been labelled "alarming" by the park's general manager Tim Faulkner given the cooler weather.

"It's extremely alarming to see one here, and we can only hope it was a once-off incident and they haven't been breeding," Mr Faulkner said in a video released to media on Thursday.

Cane toads, known for their spread across the northern parts of Australia after they were introduced to Queensland in the 1930s, have established themselves north of Coffs Harbour over the last 20 years.

It's believed the cooler weather south of Coffs Harbour has stopped them from moving lower into NSW, making sightings of them farther south rare.

An increase in sightings has led to concerns the species may be adapting to the weather in lower eastern parts of NSW.

Once the amphibians breed, they produce millions of tadpoles and if they adapt to the cold, they threaten native wildlife across NSW, Mr Faulkner added.

"If the toads can overcome that and move south, our native wildlife will face immense threat," he said.

"Catastrophic decline and near-extinction events of native wildlife have occurred due to the cane toad."

When attacked or bitten by prey, the toads excrete a venom that kills any animal that tries to harm them.

Three cane toads were spotted in the Hunter region earlier this year with one of them killing a pet dog.

The NSW Department of Primary Industries said the amphibians are sometimes accidentally transported from Queensland or north east NSW to other parts of the state.

Any sightings should be reported to the DPI and photos of the animal should be submitted to the department for identification.

Carefully capture the animal wearing gloves, glasses and long sleeves and place it in a ventilated container with a little water, a DPI spokesman told AAP in a statement.

The DPI warns people should refrain from harming the animal as it might be a native frog.

Australian Associated Press