Resident Paul Cavanagh said his nephew and son-in-law picked the injured woman up and took her to hospital after seeing she was missing her arm..
"She was standing on the side of the road just shocked," he said.
"She's lived here a long time, hopefully she's all right."
Police cordoned off the area but by the time wildlife officers arrived, the animal had disappeared.
A Department of Parks and Wildlife spokeswoman said the creature was believed to be a saltwater crocodile, which can grow up to 23 feet long and weigh more than a tonne.
Crocodiles are common in Australia's tropical north where numbers have increased since the introduction of protection laws in 1971, with government estimates putting the national population at around 100,000.
They kill an average of two people each year in Australia.