Seven people, including four children and three adults, have been found dead at a home near Margaret River in Western Australia’s South West.
Police have confirmed they are treating the deaths as a murder-suicide.
The situation is the worst mass shooting in Australia since the 1996 Port Arthur massacre, in which 35 people died and another 23 were seriously injured.
WA Police Commissioner Chris Dawson said officers were called to the rural property in Osmington, about 20 kilometres north-east of Margaret River, about 5:15am today.
Two adults were found outside the house and the other five bodies were discovered inside.
The ages of the children and adults have not been revealed.
Detectives from the Homicide Squad and Forensic Crime Scene Unit have travelled to the scene as part of the investigation.
Commissioner Dawson announced the discovery at a media conference in Perth, describing the deaths as a “horrific incident”.
He said a “male person” connected to the property had phoned police just after 5:00am, and officers arrived at the scene shortly afterwards.
Prior to this incident, the worst mass shooting — defined as a shooting involving five or more victims — since Port Arthur involved a man killing himself and four members of his family on a rural New South Wales property in Lockhart in 2014.