Three people have died after an incident in a Sydney home, with police saying they are believed to be the parents and brother of a 32-year-old man who has been arrested.

New South Wales police arrived at the house in Rosemeadow in Sydney’s south-west on Sunday just after 1.30am after reports of an assault.

A woman, 65, and a man, 25, died at the scene. A man aged 64, found with critical injuries, was treated by paramedics at the scene but later died in hospital.

They are believed to be the parents and brother of the man in custody.

Supt Grant Healey, commander at Campbelltown city police area command, said it appeared those involved were all family members.

A third son, aged 30, who was also injured during the incident, was taken to Liverpool hospital where he was treated and discharged.

Healey said the surviving family member had made the call to police.

Police suspect there could be more than one type of weapon involved, based on the injuries. No firearms were involved.

Police were “confronted with a very bloody scene”, Healey said.

“Blunt force trauma is always horrendous for people to confront, and any edge weapon attack is always horrendous to confront.

“The information we have at the moment, the family weren’t known to us. This is a very tragic incident and there was no way for us to predict this type of thing was going to occur.”

The man under arrest allegedly left the scene before returning, and Healey urged anyone who had seen a silver sedan in the area at the time to contact police.