Australian police found up to five dead people including a woman and children on Sunday in a suburb of the western city of Perth, a senior officer said.
Assistant Commissioner Paul Steel of the Metropolitan Region described the incident as a "heartbreaking tragedy".
Police have blocked off the road near the home on Coode Street in Bedford.
He confirmed that up to five bodies were found at the scene when police arrived in the suburb of Bedford at noon on Sunday.
That man, believed to be in his 20s, is now in custody. The Assistant Commissioner assured the community there were no on-going concerns for public safety as a result of this incident.
Forensic police officers inspect a property in Bedford, Perth after five bodies were discovered at the home.
'This is a tragic event and will have an impact on family and friends, the community, and the emergency services who first responded to the tragic scene.
"The homicide squad now have teams of detectives on the ground, accompanied by specialist forensic police who are meticulously working their way through this crime scene".
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He added police were still examining the home for evidence and could not provide further details on the victims.
Locals said children were often seen playing in the front yard of the home.
- Amelia Broun (@ameliabroun7) September 9, 2018Crime scene growing quickly in Bedford. Police holding a press conference at 3pm with an update.
"The WA Police Force will continue to apply our efforts to this matter as a priority, and the Homicide Squad will ensure a professional and meticulous investigation is undertaken", said a police statement.
He did not say how the people were killed or if any weapons were found.
Maria Manfredini, who has lived in the area for more than 30 years, said it was tragic on every level.
It also follows the deaths of seven people, also in Western Australia, when a grandfather shot dead his wife, daughter and her four children in a mass murder-suicide in May.
Just two months ago, an Ellenbrook mother and her two children were also found dead inside their suburban home.