Neighbour Mel Toilalo said she thought the noise was "a car crash" because it was so loud.
"I ran outside ... I saw a man on the floor, he was screaming 'she is dead' or 'she has shot herself'," Toilalo said.
"She was screaming it was his fault because he had a gun in the house."
Toilalo said the girl's mother came out of the house and was arguing with a man, who was later seen sitting in the gutter with his head in his hands.
Daily Mail Australia reported a woman shouting "I hate you, I hate you!" from an ambulance at the scene. "I hate you. He killed my baby girl," she screamed.
Fairfax reported she could also be heard screaming "not my baby girl, not my baby girl" and "rot in hell".
She said the family had moved into the house about six months ago.
Detectives from Quakers Hill Local Area Command swarmed on the home as they launched a major investigation into the girl's death. Police were seen speaking with the girl's distraught family while neighbours said the young girl's mother was "hysterical".
One neighbour said he ran outside to "chaos" with people running around and crying. He helped neighbours take three children from the house into a nearby property.
The mother of the girl then came into the neighbour's house and was "hysterical", he said.
"We were there with the kids for some time." The man said at one point the mother of the girl came inside and was extremely distressed.
"The mum came into the house and it was chaotic and all of that," he said. "She was just rambling, she was hysterical."
The neighbour said he could not believe what had happened. "It's very upsetting, we've got children of our own who are the same age range. It is traumatic."
Forensic officers arrived at the property about 10.40pm.
Earlier, a woman, believed to be the girl's mother, was escorted to an ambulance and taken from the scene. The girl's death was the most shocking incident in a night of violence in Sydney, with a man wounded in a separate shooting at Lane Cove about 10pm.
WHERE TO GET HELP:
If you are worried about your or someone else's mental health, the best place to get help is your GP or local mental health provider. However, if you or someone else is in danger or endangering others, call police immediately on 111.
OR IF YOU NEED TO TALK TO SOMEONE ELSE:
• LIFELINE: 0800 543 354 (available 24/7)
• SUICIDE CRISIS HELPLINE: 0508 828 865 (0508 TAUTOKO) (available 24/7)
• YOUTHLINE: 0800 376 633
• NEED TO TALK? Free call or text 1737 (available 24/7)
• KIDSLINE: 0800 543 754 (available 24/7)
• WHATSUP: 0800 942 8787 (1pm to 11pm)
• DEPRESSION HELPLINE: 0800 111 757
This story was originally buy the Daily Telegraph Au
