They found seven people dead on the property, including four children.
The bodies of four children and three adults were discovered in the town of Osmington, 280km (170 miles) south of Perth, on Friday.
"The bodies of two adults were located outside, five bodies were located inside a building on the rural property".
Dawson said firearms were also found at the scene.
"I can only describe it as a horrific situation", Dawson said.
Detectives from the major crime squad are travelling to Margaret River from Perth.
Specialist units from Perth have been called to the incident, including the Homicide Squad and Forensic Crime Scene Unit.
"We have no information to say there are any other public safety concerns at this stage". Police located seven persons deceased. "I will take questions but, as I've said, there's little more that I can add at this point in time", he said.
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The bodies were found on a rural property in Osmington just after 5.15am (local time).
Osmington is a sparsely populated town about 20km from Margaret River, a popular tourism area.
"It is still very early in this investigation but based on what we do know this is clearly a significant tragedy", he said.
"This devastating tragedy will no doubt have a lasting impact on the families concerned, the whole community".
Officers are now trying to locate next of kin.
"There was nothing much I could tell them", said the semi-retired farmer.
WA Police Commissioner Chris Dawson is expected to address media with details shortly.
WA police chief commissioner Chris Dawson.