Australian park rangers believe they have stumbled upon a record-breaking giant toad deep in a rainforest.

Dubbed "Toadzilla", the cane toad, an invasive species that poses a threat to Australia's ecosystem, was spotted by shocked park ranger Kylee Gray during a patrol in Conway National Park in Queensland state on 12 January.

Ms Gray and her colleagues caught the animal and brought it back to their office, where it weighed in at 2.7kg - nearly the weight of a newborn human baby.

"I reached down and grabbed the cane toad and couldn't believe how big and heavy it was," she said.

"A cane toad that size will eat anything it can fit into its mouth, and that includes insects, reptiles and small mammals," she said.

Guinness World Records lists the largest toad at 2.65 kg, a 1991 record set by a Swedish pet.

"We considered naming her Connie after Conway National Park but Toadzilla was the one that just kept getting thrown out there, so that kind of stuck," Ms Gray said.

Ms Gray's colleague, senior park ranger Barry Nolan, said the animal was euthanised due to its "ecological impact" - the usual fate for the toads across Australia.

Cane toads were introduced to Australia in 1935 to control cane beetles and other pests but their population exploded and with no natural predators they have become a threat to Australian species, Mr Nolan said.

"A female cane toad like, potentially Toadzilla, would lay up to 35,000 eggs. So their capacity to reproduce is quite staggering.

"And all parts of the cane toad's breeding cycle are poisonous to Australian native species, so prevention is a big part of how we need to manage them," he said.

Toadzilla's body was donated to the Queensland Museum for research.