The teenager charged with murdering three of his family members in Perth, has been named as Teancum Vernon Peterson-Crofts.

Perth is mourning a mother and her two children, believed to be Kiwis, who were killed at a residential home in Ellenbrook.

A GoFundMe page has been created for the family who friends say cannot afford three caskets.

The mother, 48, was described by the page's creator as someone who had faced rough times but who loved those around her.

"She was kind, happy, loved her kids, all of them unconditionally," the page read.

"She was always good to me, always supported me, always made me feel like a better person."

The 19-year-old who has been charged with the homicides had called police to a 7-Eleven convenience store on The Broadway about 1.30am.

Discussions with the teenager led police to the "horrific crime scene" nearby.

On arrival, police found the mother and her son dead inside the home. The woman's daughter was outside the home with critical injuries.

The girl was rushed by ambulance to the Royal Perth Hospital but died on the way.

The teenager has been charged in relation to the triple homicide, according to Australian news outlets.

A New Zealand Ministry of Foreign Affairs & Trade spokeswoman said it had not been approached for consular assistance in relation to the incident.

Ellenbrook resident Sarah Bell, formerly of Roturua, told the Herald the deaths had shocked and saddened the community.

Bell lives not far from the property and said there had been a heavy police presence since yesterday.

"There were neighbours out on the streets, all in disbelief," she said.

"You just don't imagine something like this happening."

Ellenbrook was a lovely neighbourhood filled with a lot of brand new houses, she said.

Western Australia Police Assistant Commissioner Paul Steel said the home and the convenience store were being investigated as crime scenes.

"This is a terrible tragedy for the family involved, for their extended family and for those first responders who were forced to attend what was a horrific crime scene," Steel said.

A senior homicide squad investigating officer told Steel it was possibly the "most horrific crime scene" he had been called to.

"My heartfelt condolences go out to all of those who have been affected by this tragic incident.

"It's a crime that I know will send shockwaves throughout the community of Western Australia."

Western Australian police were applying all resources to get to the bottom of what happened, he said.