File photo: African News Agency (ANA)

Canberra - A search is underway for a 12-year-old boy after a young family was found dead near their broken-down vehicle in the remote Australian outback, police said Thursday.

The bodies of two adults, both 19, and their three-year-old son were found late on Wednesday on a remote road near Willowra, about 300 kilometres north of Alice Springs in the Northern Territory.

An extensive land and air search is now underway for a 12-year-old who is believed to have been a passenger in the vehicle, after police received information from other family members. 

Police could not say whether the boy was related to the dead family.

"At this point, we hold grave concerns for the welfare of this child," superintendent Jody Nobbs told reporters Thursday. 

The family were last seen leaving Willowra on Friday and were bound for Yarra Yarra. The three bodies were found about 4.5 kilometres from the vehicle, along with remnants of food and water. 

Police said the deaths are not being treated as suspicious and ruled out a car crash, but they are investigating whether it was heat-related. 

According to Australia's Bureau of Meteorology, temperatures in the region exceeded 40 degrees Celsius in recent days.

"One of the avenues we are looking at is that they have walked off from a vehicle in extreme weather and may have got caught out," superintendent Shaun Gill told the Australian broadcaster ABC.

In the past fortnight, there have been two other deaths related to suspected exposure and dehydration in northern Australia.