The mother of a young British backpacker who disappeared after setting out on a run in the Queensland outback is urging police to widen their search.
Sam Woodhead was reported missing from a cattle station after he failed to return from a jog two days ago.
Local authorities launched a hunt for Woodhead amid fears he may have lost his way in the hot, isolated region in central Queensland.
Neighbours have searched the area in their own small planes, while helicopters, quad bikes, motorbikes and four-wheel drives are also being used to help find him.
His frantic mother is understood to have urged police to widen the search on the grounds that her son, an experienced long-distance runner, could have travelled some way from his base, near the town of Longreach.
His sister, Rebecca, issued an anxious plea for news on Facebook.
"If anyone hears from my brother please contact me ASAP," she wrote.
In another posting, she added: "Thanks so much for all your messages regarding Sam.
"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. will keep you all posted."
Woodhead, reportedly 18 years old and from Richmond Upon Thames, in Surrey, had been in Australia for eight days before he disappeared on Tuesday afternoon.
The former Brighton College student was reported missing by the owner of Upshot Station, where he was working.
His wallet is understood to have been found at the cattle ranch but there was no sign of his backpack or running shoes.
A Foreign Office spokesman said: "We are aware that a British national has been reported missing in Queensland, Australia.
"Consular staff in Brisbane are in contact with Australian police who are conducting the search.
"We are providing consular assistance to the family in the UK at this difficult time."
Temperatures have been about 37C in the area this week.
Speaking on her 21st birthday, Rebecca said her brother had found it "hard work" since arriving at the station.
"Sam left me a Facebook message on Monday saying he would get on Skype for my birthday. He found it hard work being on the ranch, but enjoyed riding horses and quad bikes - he's a fitness junkie," Rebecca told London's Evening Standard newspaper.
A cousin has travelled to Australia from Hong Kong to join the search and Woodhead's mother, Claire, 54, is en route from Britain, the newspaper reported.
"We're all distraught," said father Peter, 62.
"The next 48 hours are critical because we're now into his third day out there. Injury is a possibility and the police have no particular leads."
Queensland police Sergeant Dave Perry told the Standard: "It's possible he may have been jogging and become disorientated."