Police were on Sunday night yet to confirm the identities of the deceased but it is believed they are a mother, her three children and another older female relative.
The man, who is in custody being questioned, is known to the victims.
Police have not revealed what he told officers when he turned up at the police station but Assistant Commissioner Paul Steel said there were no ongoing concerns for public safety over the “tragic incident”.
They said a couple and their three children, a three-year-old girl and 18-month-old twin girls, lived at the home but that they had not seen them in recent days.
Neighbour Desrae Cambos said the family, which seemed close-knit, had lived at the house for about four years with the father running a lawn-mowing and landscaping business.
Mrs Cambos said she had assumed the family had gone away on holiday because she had not seen the father’s ute parked in the driveway since last week.
Homicide detectives are investigating the deaths and both Coode Street and adjoining Fort Street remained locked down last night as forensic officers examined the property.
The police chaplain was at the scene to give support to officers involved in the gruesome discovery and investigation.
Mr Steel said it was still unclear how long the bodies had been at the house before they were discovered.
“Sadly, at that location, police have located the bodies of a number of deceased people, including women and children,” he said.
“This is a tragic event that will have no doubt have an impact, not only on the family and friends of the deceased, but for the whole of the community, those first responders who were faced with attending a scene with multiple deceased people. It does send a ripple through the community of Western Australia.
“Part of the homicide squad investigation is going to try and identify the time line of all events which led to this matter. How long the bodies have been there will also form part of that timeline inquiry.”
Mr Steel said it was expected the crime scene examination could take “a number of days” and would involve specialist forensic police officers.
He would not name the regional police station the man went to because of the “highly emotive” nature of the situation.
The cause of deaths are yet to be determined by police.
Vagner De Souza, who lives across the street, said the tragedy had stunned residents in the area.
“It is pretty crazy, I always park my car over there,” he said.
“I would see the family there with the guy doing his yard. They just looked like a normal family.”
Maria Manfredini, who has lived in the area for more than 30 years, said it was tragic on every level.
“I am deeply saddened by what had happened today,” she said.
“We are a very close community, we have a high school just a few hundred metres and the street is always so calm and peaceful. It has taken everyone by surprise, we are all in complete shock.
“It is something you never would think would happen in this area,” she said. “It is safe, we have grown up all our lives and this is just so sad and horrific.”
“ We would say ‘hi’ when we were walking past and is sad that something like this would happen.”
This article originally appeared on PerthNow.