A British student on his gap year has gone missing in the Australian outback after going for a run.

Sam Woodhead, 18, has been missing since Tuesday and search and rescue are becoming increasingly concerned for his wellbeing as daytime temperatures soar to 39C.

Woodhead, from Richmond, Surrey, is described as a fitness fanatic. Police believe he may have gone for a run and become lost or injured in the bush.

Senior constable Shane Ranger told the Brisbane Times that snakes and the blistering heat were a major concern. "We just don't know what he has got with him out there," he said.

"Dehydration, snakebite, injury - those are the factors we are concerned about."

Sam Woodhead
Woodhead is described as a fitness fanatic and is thought to have gone for a run (Facebook)

Woodhead was last seen at a ranch called Upshot Station, where he had been staying. A search of his room revealed that his running shoes and backpack were missing but his wallet had been left behind.

Sgt Dave Perry said: "The owner of the property had gone to probably chase him out of bed. She went to his room and he was not there.

"There's no indication of anything that would cause him to go away.

"He's really into fitness. It is possible he may have been jogging on this occasion and become disoriented.

"We're not basing that on anything other than the fact he's been jogging previously."

Sam Woodhead
The student\'s sister, Rebecca, is keeping friends and family updated online (Facebook)

Woodhead had been a student at Brighton College and had been visiting the Gold Coast as part of his gap year. His sister, Rebecca, has been keeping friends and family updated on the search progress on Facebook.

She said: "Still no further news but we have the helicopter going out again in the morning, Aus time, and hundreds of people going on a voluntary search party.

"Would be a great birthday present if my brother would just turn up and ask what all the fuss is about."

Upshot Station is in a remote area, around 80 miles from Longreach. The land covers around 3,200 acres.