A young Australian woman has completed an ultra-marathon across the country's Simpson Desert for charity, local media reported on Friday.

Graduate lawyer Samantha Gash, 27, left from a remote area of the Northern Territory on Monday morning, crossing 379 kilometers to finish at Birdsville in Queensland's far-west late on Thursday night, the Australian Associated Press (AAP) reported.

The motivation behind the journey is to raise 69,000 AU dollars (71,760 US dollars) for the charity Save the Children to support its program providing playgrounds for children and their parents in some of the most disadvantaged communities in Australia.

She told AAP on Friday that it was tough to deal with the sleep deprivation and physical exhaustion during the journey.

"Let's just say the last few kilometers were the hardest," she said.

A support crew of eight took turns to run alongside her.