A man has been charged with murder after he allegedly used a hammer or similar blunt weapon in a deadly attack on his mother, father and little brother.

Jacky Feng, 32, is accused of attacking his parents and two siblings at their family home on Juliet Close in Rosemeadow, southwest Sydney, shortly after 1.30am on Sunday. The second brother survived the attack.

NSW Police will allege Feng left the scene and returned an hour later to find emergency services swarming the property.

The 32-year-old was charged with three counts of murder and one count of attempted murder on Sunday night. He was refused bail and is set to front Campbelltown Local Court on Monday.

Emergency services were called to the home following reports of a violent assault, however, they were confronted by a 'very grisly crime scene' upon their arrival.

'Police first encountered a 65-year-old woman and started doing first aid on her... police went inside the house and found a 64-year-old male who was still alive with serious blunt force head injuries,' Campbelltown Commander Superintendent Grant Healey said.

'They found a male deceased in a granny flat at the rear of the premise.'

It's understood the man was the family's youngest son, who was 25-years-old.

Superintendent Healey said the second brother, aged 30, contacted emergency services after he was allegedly assaulted. 

He was taken to Liverpool Hospital and was released after receiving medical treatment on Sunday morning.

Officers arrested the 32-year-old man an hour after the grim discovery when a silver sedan pulled up at the scene.

Superintendent Healey said the family, who are Asian-Australians, were not well known to police.

'This is a very tragic incident, there was no way for us to predict this type of thing was going to occur,' he said. 

'This is an incredibly rare incident and it's incredibly tragic.'

Supt Healey earlier said police believe more than one weapon was used during the deadly attack, one that would cause 'blunt force trauma' as well as a 'bladed weapon'. 

No firearms are believed to have been involved.

As police worked to tow away the silver sedan on Sunday morning, shocked neighbours told the Daily Mail the family mainly 'kept to themselves'.

One neighbour, who knew the family's eldest son, said ambulance crews had attended the home several times in the last year. 

Another neighbour said he was awoken at 1.30am by the sounds of what he thought was 'a car chase.'

'Then all the emergency cars came and a silver Subaru returned to the street. Someone said they saw a man hold up his hands as police approached him,' he said.

As investigations continued into Sunday afternoon, forensic officers were seen taking a thermal imaging camera into the house and transporting evidence from the scene.

At 2.35pm a white Coroner's van arrived in the street and reversed into the driveway of the home. 

Two empty stretcher trollies were wheeled into the premises. 

Over the next 15 minutes the trollies, each loaded with a body, were wheeled out and placed into the white van which left the scene just before 3pm.