WARNING: Graphic

A woman will be assessed in hospital after she allegedly decapitated her mum with several knives in front of the 57-year-old's grandson in their western Sydney home.

Jessica Camilleri, 25, faced Parramatta Bail Court today charged with murder after she allegedly attacked her mum Rita in their St Clair home late last night.

She did not apply for bail, with her lawyer telling the court she had significant health issues and an order was made for her to be assessed in hospital before her next court appearance.

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Camilleri, who appeared in court via video link, said she couldn't move her fingers after what had happened or wash herself properly to get all the blood off.

It's alleged the 25-year-old used a "number of knives" to kill her mother and cut off her head — before dropping it on the footpath outside their family home just after 11.30pm last night.

Support is being provided to the first responders who witnessed the horrific scene with police describing it as "as bad as it gets".

Police allege Rita was killed by her daughter in the kitchen of their family's St Clair home, where they both lived, before the 25-year-old carried her head two houses down the road.

Police at the scene in St Clair last night. Photo / Supplied
Police at the scene in St Clair last night. Photo / Supplied

Speaking to reporters this afternoon, Nepean Police Area Commander Detective Superintendent Brett McFadden said "this is up there with one of the most significant, most horrific scenes police have had to face".

Police rushed to the St Clair Ave home just after 11.30pm last night to reports of two women arguing.

Rita Camilleri was killed last night. Photo / Facebook
Rita Camilleri was killed last night. Photo / Facebook

McFadden said the information they received from neighbours was "quite specific".

News.com.au understands neighbours started to rush to the aid of the mother after hearing the "violent argument" but were instead confronted by the 57-year-old's head on the footpath.

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A NSW Police spokeswoman said the boy was treated at Westmead Children's Hospital and was released to the care of other family members.

She described the scene as "distressing".

The young boy is not the 25-year-old woman's son, police said.

The footpath outside the St Clair home. Photo / News Corp Australia
The footpath outside the St Clair home. Photo / News Corp Australia

Officers rushed to the scene and found the mum's head and later found the rest of her dismembered body inside the kitchen of their St Clair Ave home.

McFadden said the mum had suffered "extensive injuries".

"We understand at this stage that a number of knives were used during the course of the incident. I am not able to specify what kind of knives they were at this stage. They both reside at the home together," he said.

The woman's 25-year-old daughter was arrested in the front yard of a neighbour's home.

"There is no stepping away from the fact that this was horrific and a significant attack," McFadden said, commending the professionalism of police.

A police officer stands outside the St Clair home. Photo / News Corp Australia
A police officer stands outside the St Clair home. Photo / News Corp Australia
Dozens of police officers have been canvassing the scene. Photo / News Corp Australia
Dozens of police officers have been canvassing the scene. Photo / News Corp Australia

McFadden said the 25-year-old was known to police but "there was no information that this situation in the family home was likely to occur".

Camilleri was caring for her four-year-old grandson when she was allegedly murdered by her daughter.

The four-year-old was taken to Westmead Children's Hospital with a small head injury and is now being cared for by his family.

McFadden said the boy had witnessed the alleged crime.

"The family is distraught as to what has taken place," he said.

A knife was seized for forensic examination and several crime scenes have been established inside the home, police said.

Detectives have established a strike force to further investigate the incident.

The 25-year-old will face Parramatta Local Court later today, charged with one count of murder.