A search is under way for a 71-year-old woman missing in the Northern Territory's Litchfield National Park.
The woman failed to return on Sunday from a bushwalk near Wangi Falls, about 110km south of Darwin, NT police said.
Rescue specialists, police and park rangers started searching on Monday morning.
Superintendent Brendan Muldoon urged travellers in the area to keep an eye out for the woman.
"She is reportedly a fit and experienced hiker. However, the terrain is challenging out there and we have concerns for her safety," he said.
The minimum overnight temperature in the park was 19C, with a maximum of 32C.
Much of the terrain near Wangi Falls is thick bush and hilly.