A man is in custody after three people died in a home in Sydney’s south-west overnight in an alleged attack.

It was initially reported the trio were assaulted by someone known to them in the early hours of the morning at a home in Rosemeadow, with emergency services arriving at the house on Juliet Close just after 1.30am.

Inside, they found a 64-year-old man with serious head injuries, and the bodies of a man and a woman.

Authorities were called to the home at 1.30 this morning.© Nine

The bodies found in the home are believed to be of a man in his 20s and a woman in her 60s.

They have not been formally identified.

Two people died inside the home, while a man, 64, later died in hospital.© Nine

A man was arrested after returning to the home at 2.30am in a silver sedan.© Nine

The injured man was treated by paramedics at the home and was taken to Liverpool Hospital, but he later died.

About an hour later, a silver sedan arrived at the home, and police arrested the driver, a 32-year-old man.

He was taken to Campbelltown Police Station pending further inquiries, but has not been charged with any offences.

A crime scene has been established, with officers connected to the Homicide Squad beginning an investigation.

A report will be prepared for the coroner.

Anyone with information on the incident is urged to contact Crime Stoppers.