Seven people have been found dead at a rural property near Margaret River in Western Australia (WA), police say.
The bodies of four children and three adults were discovered in the town of Osmington, 280km (170 miles) south of Perth, on Friday.
Authorities would not say how the victims died, but confirmed that two firearms were found at the scene.
There was no ongoing threat to public safety, police said. They would not confirm reports of a murder-suicide.
“The bodies of two adults were located outside [and] five bodies were located inside a building on the rural property,” said WA Police Commissioner Chris Dawson.
“It appears that gunshot wounds are there, but I don’t want to go further than that.”
If confirmed to be a mass shooting, it would be Australia’s worst since a massacre in Tasmania claimed the lives of 35 people in 1996.
Authorities said names and ages of the victims would not be disclosed until next of kin had been notified.
However, Mr Dawson said they were believed to have lived at the property.
“The loss of any life is tragic, but four children and three adults – this is a significant tragedy,” he said.
Authorities were called to the scene at 05:15 local time (21:15 GMT on Thursday) after receiving a call from a “male person”, Mr Dawson said.
The commissioner did not give details of the call, but said it had been recorded.
He said specialist police officers from Perth would oversee a large-scale investigation.
Osmington is a tiny rural community about 20km from Margaret River, a popular tourist and wine-growing area.
One neighbour, Felicity Haynes, described the residents of the property as “lovely people”.
“They were a very socially-aware family – doing their best to create a safe community – and that is why it is so shocking to think that could be destroyed so quickly,” she told the Australian Broadcasting Corp.
Local shire president Pamela Townshend told Fairfax Media: “It’s sending shockwaves through the whole community – we’re all linked in one way or another, every family.”
After the 1996 massacre at Port Arthur in Tasmania, Australia enacted strict gun laws that banned automatic and semi-automatic weapons.
It has had one other mass shooting since Port Arthur – the murder-suicide of a family of five in New South Wales in 2014.