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

The 19-year-old who accused of murdering a mother and two of her children appeared to have a psychotic episode in a Perth court.

Petersen-Crofts, who is related to what is believed to be a Kiwi family, fronted Midland's Magistrates Court today without a lawyer, the Canberra Times reports.

He has been sent to a mental health facility, Franklin Centre Graylands Hospital, until his next court date on July 23.

The 19-year-old had called police to a 7-Eleven convenience store on The Broadway about 1.30am.

Inquiries led police to the "horrific crime scene" nearby.

On arrival, police found the mother and her 8-year-old son dead inside the home. The woman's daughter was outside the home with critical injuries. The 15-year-old was rushed by ambulance to the Royal Perth Hospital but died on the way.

Australian media has reported that police were seen taking a large pair of scissors away from the crime scene.

The 19-year-old has been charged in relation to the triple homicide, according to Australian news outlets, was due to appear in court today.

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

Ellenbrook resident Sarah Bell, formerly of Rotorua, 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 shock waves throughout the community of Western Australia."

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