A 16-year-old boy has been charged with murder after his father was stabbed to death at the family's north-west Sydney home, police say.
The boy, whose mother was also injured in the early morning attack, has also been charged with attempted murder, police said.
The badly wounded mother, aged 50, is thought to have phoned triple-0 for help about 7am.
The woman has emerged from surgery at Westmead Hospital after suffering abdomen and back wounds.
Police arrived at the two-storey brick home in a cul-de-sac in Baulkham Hills in Sydney's north-west, and found the father and mother suffering from stab wounds, a police spokesman said.
The 57-year-old man was dead when police arrived.
Police earlier informed the media the woman died at Westmead Hospital about 11.45am as a result of abdomen and back wounds she suffered in the attack.
"We have just been told that the woman is not dead," a police spokeswoman said.
"We were told she was [dead] ... but we have just had that source come back to us and say that she is still in surgery and she was given the wrong information."
Local area police Commander Sue Waites said police had to restrain the "aggressive" boy, who was in the front yard with a school bag and about to leave.
"There was an altercation with police. He was then handcuffed and detained in the front garden," Superintendent Waites said.
The boy did not have a weapon with him when he was arrested, she said. A knife was found at the house.
She said it was "a pretty horrific crime scene".
The woman had been dressed for work at the time of the attack, she said.
She and her husband were attacked in separate rooms on the ground floor of their house
A neighbour said the mother had worked in administration at Westmead Hospital.
A neighbour, Chitra Iyer, said she was stunned by the attack.
"They were like family to us. I can't believe it," she said.
The family had moved to the cul-de-sac in 1992 and had become firm friends with the Iyers, she said.
The father, who owned an electronics business, had helped the Iyers with their electronics and had set up their home computer, she said.
"There were never any problems. We never heard them fight,'' she said.
"They were very devoted parents. They'd take him everywhere, to all his activities."
The son was a keen swimmer and had recently bought a drum kit, Ms Iyers said.
"He'd saved up and bought his own kit. [His father] would take him to the shop so he could buy things for the drums," she said.
Neighbour Jennifer Moore said her son and daughter, 17 and 15 respectively, went to St Michael's primary school with the 16-year-old.
Ms Moore said she worked in the school canteen with the mother and described her as lovely and hard working, but her son rarely played with the boy.
She said the boy's mother was "a lovely woman" and the father was a "very respectable gentleman".
A boy who goes to the same school as the son said there was no address to the students about the killings today.
He said he knew of the arrested 16-year-old by sight and described and said he seemed to be "a normal kid who hung out with normal people''.
"We are just in shock that it happened,'' he said.
Another male year 12 student said news of the killing spread quickly at recess.