Police investigating a mass murder-suicide near Margaret River in Western Australia, in which a grandfather is suspected of killing six of his family members, today confirmed three long-arm firearms registered to the man were found at the scene.

Western Australian Police Commissioner Chris Dawson confirmed the deaths of seven people - four of them children - all from the same family, which comes as Australia's worst mass shooting since the Port Arthur massacre.

Police have named the seven people found dead in a mass murder-suicide near Margaret River, Western Australia. (Supplied) (Nine)

Peter Miles, 61, is suspected of killing his family before himself on a rural WA property. (Nine)

He also said that six of the deaths are believed to have been homicides while the body of the seventh person was found in the same location on a property in the town of Osmington, 250km south of Perth.

While formal identification of the victims is still underway, police confirmed they believe the seven dead individuals to be Peter John Miles, 61, his wife Cynda Miles 58, their daughter Katrina Miles, 35, and her four children: Taye Cockman, a 13-year-old girl, Rylan Cockman, a 12-year-old boy, Arye Cockman, a 10-year-old boy and Kadyn Cockman, an eight-year-old boy.

Katrina Miles lived at the Osmington property with her four children. (Facebook) (Facebook)

Police found a "horrific" scene when they arrived at the property early on Friday morning. (9NEWS) (9NEWS)

Commissioner Dawson also said that police called to the scene located one body outside of a building on the property, while the body of an adult female was found inside the main house and five others - a female and four children - were found in a "converted shed structure".

"I also can now confirm that police have recovered three firearms, all long-arms, at the location. All three firearms are licensed to Peter Miles," he said.

Police forensics investigate the deaths on the rural property. (AAP) (Nine)

The grandparents daughter lived at the property, where it's believed she home schooled her four young children. (Nine)

"I wish to strongly emphasis that police do not believe any other person is involved with these crimes. Police are not searching for any other suspect."

The well-kept property belonged to grandparents Peter and Cynda Miles, who were well known and respected in the Margaret River community.

Peter and Cynda's daughter Katrina Miles also lived at the property, where she home-schooled her four young children.

Cynda Miles, who owned the farm, was well known and respected in the Margaret River community. (Supplied) (Nine)

The small, tight-knit community has been left rocked by the tragedy. (AAP) (Nine)

Police received an emergency Triple Zero call from a man at 5.15am yesterday that lasted around two minutes, before arriving to the property and finding all seven people dead with gunshot wounds.

"This is a complex criminal investigation," Commissioner Dawson said.

"We are treating this as a matter in which clearly six persons are subject of a homicide crime scene. There is a seventh person deceased."

WA police chief commissioner Chris Dawson said the incident was a "devastating tragedy". (AAP) (Nine)

"They are a hugely respected family and a great asset to the community." (Nine)

The family released a statement today saying they were "devastated by this shocking event".

"We are stunned and still trying to understand how this could happen.

"We respectfully ask that the community refrain from speculating on the circumstances surrounding this tragic incident.

"We thank the community for their support and ask that our privacy is respected as we grieve."

President of the Augusta Margaret River Shire, Pamela Townsend, today also said she is "absolutely devastated" that the crime occurred in the small, tight-knit community.

Police are yet to officially name the victims, but believe they were residents of the property. (9NEWS) (9NEWS)

Forensic crews found two firearms at the scene. (9NEWS) (9NEWS)

"It's such a small community and it's already having a huge effect, because in this community we're so well connected," she said.

The local government in the area has also established sessions with counsellors and psychiatrists at the Margaret River community resource centre, where mourners can also offer flowers and their condolences.

Osmington is about 260kms south of Perth. (9NEWS) (9news)

A friend of the family, Felicity Haynes, earlier told 9NEWS that Cynda Miles was an outgoing, bubbly person who was loved by the local community.

"I feel sick to the stomach…that couldn’t happen here," she said.

"It's just horrifying. They were good people. It's not fair.

"You can imagine this warm, motherly person whose always smiling, always generous and brings fresh baked scones to everything. That's Cynda."

Just one month ago, the mother-of-four, Katrina, posted on Facebook that she believed she was being stalked by someone close to her.

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