Son in custody after man found dead in backyard of NSW home

A man is in custody after his 74-year-old father was found dead in the backyard of their home in south-east New South Wales.

Emergency services were called to a home at Farmborough Heights in Illawarra about 6pm on Sunday over reports of a man with serious head injuries.

It was there first responders found the 74-year-old dead.

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Detective Chief Inspector Brad Ainsworth confirmed the 48-year-old son, who lived at the home with his father, has been taken into custody and is assisting police with ongoing inquiries.

"We've got homicide squad with us, we've formed a strike force, we've got paws - the dog squad - down there, we're doing a canvas and an investigative search," he said at a press conference today.

Ainsworth said the 74-year-old had been lying in his backyard anytime between February 1 to February 5 until his body was discovered by a neighbour.

"Obviously distressing and disturbing for the neighbour and the first police on scene but I can assure the community and members of the public it is safe in Farmborough Heights," he said.

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"This is an isolated incident."

Police are awaiting post-mortem results to determine the cause of the man's death and will prepare a report for the Coroner.

Anyone with information or who may be a witness is urged to come forward and contact Crime Stoppers on 1800 333 000.