An aged care resident has been charged after allegedly assaulting a dementia patient, who was left with severe head and facial injuries so severe he was almost unrecognisable. 

John, 87, who suffers from dementia and lives at HammondCare's aged care facility in Hammondville in Sydney's south-west, was allegedly attacked on Wednesday night before being taken to Liverpool Hospital at 9pm.

Graphic photographs taken in hospital show the pensioner covered in blood and bruises, with both eyes severely swollen, injuries across his head and face, and a neck brace as blood appears to flow from his ear onto a pillow.

He was allegedly found bloodied on the veranda outside his cottage, located within the facility's secure dementia care unit, following the incident. 

NSW Police arrested a 69-year-old man at the HammondCare facility on Thursday at 3pm. 

A spokesperson said he was taken to Liverpool Police Station and charged with assault occasioning actual bodily harm (domestic violence).

He was later taken to the same hospital as his alleged victim, where he remains under police guard.

The 69-year-old was refused bail and is due to face Liverpool Local Court via a bedside hearing on Friday.

John's daughter, Margaret, who lives in Spain, said the family were in total shock.

'I've never seen anything like this before. I've never seen anybody this beat up,' she said on 2GB on Thursday.

'My mother received a phone call last night at 9:31pm from the night staff informing her that Dad had been hurt.

'They wanted to send him to the hospital and told Mum, no need to come, we're just going to put him in the ambulance.

'My mother, who's 85, insisted that they wait until she arrived at HammondCare at Hammondville to join my father in the ambulance.'

The distraught daughter said she was demanding answers from HammondCare.

'I have emailed the dementia supervisor and I have also emailed the person who oversees HammondCare, and I have not received a response yet, but in my email I have requested a full investigation,' she said.

'I have asked for them to retain all documentation and any logs that exist, so we can have the full documents. We want to know what happened.'

HammondCare released a statement confirming it had launched an investigation into the circumstances surrounding the alleged assault. 

'We are extremely sorry and deeply saddened that this has occurred,' HammondCare Executive General Manager Jenny Summerton said.

'Police were notified immediately of the assault and the family were also informed.

'The cottage is one of 30 SDCP cottages nationally that provide specialist care to people with very severe behavioural and psychological symptoms of dementia. 

'These are residents assessed as unable to be cared for in mainstream aged care settings.'

The statement added that a Serious Incident Report would be provided to the Aged Care Quality and Safety Commission later on Thursday.

According to the HammondCare website, its Hammondville facility includes one of the only purpose-built villages for dementia care in the Liverpool area.

The village features small, home-like cottages surrounded by gardens and incorporates design principles intended to help residents maintain their independence.