Three children, including a toddler and a baby, have died after a house fire in Sydney's west.
Four other children and a 29-year-old woman are being treated in hospital.
What's next?
A 28-year-old man has been arrested and remains under police guard in hospital.
A fire which killed three young children in a house at Lalor Park in Sydney's west is being treated as a domestic violence incident.
Fire crews were called to the scene just before 1am on Sunday.
Police said two boys, aged three and six, were treated by paramedics and taken to Westmead Hospital in a critical condition, but died a short time later.
Fire and Rescue crews extinguished the fire before the third child, a five-month-old girl who police initially said was 10 months old, was found dead at the scene.
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Detective Doherty said the mother is aware of the tragedy but is now under sedation.
"They've just survived a traumatic fire incident where they've all been impacted physically, but they've also been impacted emotionally and mentally. That is the longer-term issue.
"Hopefully they can get through the physical injuries, but the emotional and mental issues, what they have to cope with, that will be a longer term. That is where the support comes around."
Fire investigators plan to spend days combing through the site, including using an accelerant dog to determine the cause of the blaze.
"That will be part of the investigations while they rake through the scene, that will take time," Doherty says.
"This won't just happen today but over days. They are the answers we will have to provide at a later stage."
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Police allege a 28-year-old man, who is now in custody, tried to stop police and other emergency services from rescuing the children from the burning home.
"I can confirm during police attempts to get into the property, those efforts were frustrated by a male inside," NSW Police Acting Superintendent Jason Pietruszka said.
Four other children survived the fire. (Supplied)
The man arrested is the father of the children who died and was under police guard in hospital.
He was in an induced coma and being treated for burns and smoke inhalation.
The mother as well as three boys aged, four, seven and 11, and a nine-year-old girl, were also taken to hospital and were expected to recover.
Superintendent Pietruszka said the incident was being investigated as a domestic violence related offence, and said the man was not the subject of an AVO and was not before the court for any matter.
"He is not adversely known to police at all," Superintendent Pietruszka said.
"We're treating this as a domestic-related homicide, multiple homicide."
Fire investigators are making their way through the low-set brick house on Freeman Street in Lalor Park. (ABC News: Ethan Rix)
'Hero' neighbour
Superintendent Pietruszka said police will allege the 28-year-old tried to stop neighbours and emergency services as they "heroically" tried to rescue the children.
"The building was on fire, police approached, as did a neighbour, quite heroic in what they did in trying to get entry into a place that as stated was well on fire," he said.
"The neighbour did try to assist and I believe those actions, as well, saved further life from being lost."
Police will allege the father of the children tried to stop efforts from a neighbour to save them. (ABC News: Ethan Rix)
Detective Superintendent Danny Doherty from the homicide squad said the mother is aware of the tragedy but was now under sedation.
"They've just survived a traumatic fire incident where they've all been impacted physically, but they've also been impacted emotionally and mentally," he said.
"Hopefully they can get through the physical injuries but the emotional and mental issues, what they have to cope with, that will be a longer term."
Police said the children had not been formally identified.
Police are investigating whether an accelerant was used to start the fire. (ABC News: Tony Ibrahim )
Firefighters search for children under 'confronting' and 'extreme' conditions
NSW Fire and Rescue superintendent Adam Dewberry said firefighters rushed into the burning home to search for the children and were met with what he described as a "confronting" scene.
"When our crews arrived they were confronted by pretty chaotic scenes with a number of adults and children who had self-evacuated," Superintendent Dewberry said.
"They got in under those fire conditions, started to knock down the fire and conducted a search under very extreme conditions."
Dozens of police, ambulance and other emergency services were at the scene overnight.(ABC News)
The firefighters who found the two and four-year-olds went back into the home to search for the baby.
Superintendent Dewberry said temperatures likely reached between 600 and 700 degrees Celsius.
"They can't see … they're getting through under extreme, superheated conditions, while looking for those children," he said.
"The firefighters who found the two children actually went back in to conducted a search for the third child, but unfortunately they were unable to locate that child, who was located after the smoke had cleared.
"I watched a young child sitting on a young constable's lap while they were being treated by paramedics.
"This is just a tragedy all round. Everyone deals with these things differently; we've got to make sure that we are there for our firefighters, there for each other."
Local residents Graham and Elizabeth Cocks woke to news of the tragedy this morning. (ABC News: Ethan Rix)
Children deserved 'caring home'
NSW Premier Chris Minns described the incident as horrifying and senseless, promising that the state would provide support to the family.
In a statement, the premier said the children deserved "love and protection and a caring home".
"Our love and thoughts are with the surviving family members," Mr Minns said.
"Our thoughts are also with the emergency service workers who fought to save lives last night, and who will also be recovering in their own way after a horrible night."
NSW Premier Chris Minns said that love and thoughts are with the surviving family members.(ABC News: Ethan Rix)
Mayor of Blacktown City Brad Bunting said he was devastated by the news and that the council would rally around the community of Lalor Park.
"We thank fire and rescue, police, and all emergency services officers for their immediate response," Mr Bunting said.
"In the days ahead, our council will look to support the heartbroken family and local residents."
Shocked locals woke to the scene this morning.
Nearby residents Graham and Elizabeth Cocks said they were devastated by the deaths.
"It's just terrible," Mr Cocks said.
"When it happens so close to home, it's happening in the suburb we have been for 20 years, just devastating to know that this sort of thing has gone on. Just awful."