Son arrested after couple allegedly found stabbed in Sydney home

The couple allegedly killed by their son at their home in Sutherland in southern Sydney have been named as 71-year-old Diana Reid and husband Graham Reid, 75.

Their 46-year-old son, David, is expected to be charged after a horrific scene was discovered this morning.

Emergency services say they were called to the couple's home in Tudar Road, Sutherland, at 8am by David Reid.

He was threatening self harm.

However, when police went inside, the couple were found dead with what police say were stab wounds.

One body was found in the bedroom and another in the lounge room, police reported.

Detective Superintendent Jason Box described the scene which greeted offices as "very traumatic".

"Walking in and seeing that scenario was quite confronting," he said.

Det Sup Box said the family were not known to police and there we no known mental health issues.

David Reid is under police guard at Sutherland Hospital with self inflicted injuries.

"He's made certain comments to police at the scene and while he's been in the hospital and it's something detectives are following up," Detective Superintendent Box said.

Police are appealing for help if anybody saw anything unusual, and have set up a crime scene at the home.

They've also been door-knocking neighbours.

The family's next-of-kin is being spoken to by police.

"I didn't notice it until the tradesman said to me something is going on down the road. He said 'police cars have turned up'," one resident told 9News.