Twin girls, 5 and boy, 11, killed after blaze rips through home in NSW Hunter Valley

Neighbours have described how they tried to save three children tragically killed in a house fire in the NSW Hunter Valley.

Twins Matylda and Scarlett Rinkin, both five, and brother Blake, 11, lost their lives in the blaze in Singleton.

Heroic neighbours tried to use garden hoses on the fire, before fire crews managed to rescue mum Kara Atkins, 31, and daughter Bayley, 8.

The twins died in hospital, with Ms Atkins and Bayley also rushed to John Hunter Hospital suffering burns and smoke inhalation.

The mother and Bayley today both remain in a serious but stable condition.

Neighbours had reported they heard smoke detectors going off and the sound of breaking glass caused by the fire after it broke out at 3.30am.

“I was woken up to screams. I could hear things exploding,” one neighbour told 9News.

“I saw Kara come out, All I saw was her eyes and how wide they were. She was just crying.”

Another neighbour told 9News how she heard screams as the fire broke out.

"It was terrible. It was horrendous.”

Hunter Valley Police District Commander Superintendent Chad Gillies said emergency services and the community have been left devastated.

He said the house was well engulfed by flames by the time emergency services arrived.

"What I can say is that in the efforts of trying to put the fire out, four residents have assisted and removed the mother - a 31-year-old lady, and an 8-year-old daughter from the house, safely," he said.

"Two 5-year-old girls were removed from the house by Fire and Rescue staff and subsequently taken to Singleton Hospital. Tragically, they were pronounced dead at Singleton Hospital."

He also said an 11-year-old boy was later found dead inside the property.

He praised the "heroic nature" of the four residents who tried to assist the people inside the house and helped get the mother and girl out.

Fire and Rescue NSW Superintendent Joshua Turner said fire crews arrived to find neighbours desperately trying to put out the flames with hoses.

"They made entry through the front door, but unfortunately, the heat and the intensity of the fire made them force their way back through the front door and have to go into what we call a defensive mode, which is fight the fire from the outside."

Crews managed to access the side of the house through side windows into two bedrooms that weren't yet completely engulfed and removed two people.

However the intensity of the fire and the risk of the structure collapse meant they could not continue.

Hours after the blaze, family friend Caitlyn Stemmer began a crowd-funding campaign, posting pictures of the children online, and has since passed $90,000 in donations.

She said the tragedy would hit the community hard.

"The whole town is devastated by the news," she told AAP.

"It'll be a hard thing for everyone to get past."

Police will prepare a report for the Coroner outlining the full circumstances surrounding the incident.

Investigations are continuing to determine the cause of the blaze and authorities are also looking at whether a combustible fireplace may have played part in sparking the inferno.