A mother and child safely escaped a Keysbrook home where her partner was shot dead on Saturday, homicide detectives have revealed.

The fatal shooting unfolded on Saturday morning at a rural property on Scarp Road, about 73km south-east of Perth.

The woman, in her 40s, and her son fled to a neighbour’s for help, who raised the alarm with authorities that a man had been critically injured, about 8.40am.

Significant police resources were sent to the area, including tactical officers, where they found a 44-year-old man shot dead inside the property.

A 38-year-old man, who police say was known to the victim, was found inside a parked vehicle at the property shortly after. He was arrested and is assisting police with their inquiries.

Homicide squad detective senior sergeant Stephen Cleal said police were still determining the relationship between the man in custody, 38, and the victim, 44. He confirmed the victim and the woman at the scene had been in a relationship.

Armed officers were seen searching the outbuildings on the property as detectives flooded the scene.

Police were later seen walking the woman and child out of the residence and down the driveway.

The distraught woman was dressed in a blue forensic jumpsuit and the pair got into the back seats of an unmarked police car before it drove away.

Det-Sen. Sgt Cleal said while the woman and child were uninjured, they had experienced a horrific event.

“They are in with one of the crew from my team and with police at the moment. I can tell you that they’re uninjured, but I can also tell you that they’ve been confronted with something very horrific,” he said.

“My thoughts are with them at the moment . . . I’m glad they were not injured, but what a terrible thing for them to go through.”

Blue and white police tape cordoned off the residence from the top of the dirt turnoff into Saturday evening, as homicide detectives and forensic crews continued combing through the rural property in a bid to piece together the moments before and after the fatal shooting.

Among the evidence already gathered is a firearm police found at the property.

It is understood the man in custody was not a licensed firearm holder, but was cooperating with police on Saturday afternoon.

Det-Sen. Sgt Cleal warned the investigation could take some time due to its complexity.

“There’s a fair bit going on at the moment, as you can imagine,” he said.

“I’ve not given forensics any timeline to work towards, this is going to be significant, this is going to be thorough, and this is going to take time.

“We could be here (in Keysbrook) for days, I don’t know at this stage until I know exactly what we’re confronted with, and for that I rely on the forensic experts who do a fantastic job.”

The property is an old orchard surrounded by dense bushland.

Det-Sen. Sgt Cleal commended the first responders who attended the scene.

“What happened today is a difficult response, they’re our specialist unit designed to deal with incidences of firearms and first responders, they never know what they’re walking into,” he said.

“Here’s another example of that, they do a great job.”

The homicide squad are investigating the incident and urge anyone with information to contact Crime Stoppers on 1800 333 000 or by making a report online.

Information can be provided to police anonymously.