A 5-year-old Sydney boy is dead after being stabbed with "horrendous violence" during a dispute at his home in a crime police say is as bad as it gets.
His distraught grandmother, aged in her 60s, tried to take the child to safety before realising the extent of his injuries and calling police and emergency services to the home in Carlingford around 7am on Friday.
Paramedics performed CPR and the boy was rushed by police escort to Westmead's Children's Hospital in a critical condition but died about an hour later.
"The level of violence is horrendous," NSW Police Superintendent Rob Critchlow told reporters at the crime scene in Sydney's north west.
"A young boy has died from being injured in his home, it's probably about as bad as it gets, really."
A 36-year-old man, who was known to the boy and known to police, has been arrested.
Supt Critchlow said the grandmother, who wasn't injured in the attack, did what "every grandmother would do".
"She's behaved in a heroic and caring manner. She's been presented with something terrible and done her best to get the young boy to safety and to get him treatment.
"Sadly, despite her best efforts, there was nothing more she could have done."
Paramedics have treated the grandmother for shock.
The child's mother, who was not at the home when the attack happened, is being supported by medical professionals at the hospital where her son died.
Police say they have the weapon used on the boy.
"It was a sharp weapon - we believe a knife," Supt Critchlow said.
Two crime scenes have been set up, at the home on Paul Place and nearby Moseley St.
The man is expected to be charged, Supt Critchlow said.
