The horrific series of events began with the stabbing of the man's grandparents at their home on East Street, Bega, about 3.30pm on Friday.

After the man allegedly fled in his grandparents' car, his 71-year-old grandfather stumbled outside and flagged down a passing motorist who called triple-0.

Police arrived at the scene to find the man and his 69-year-old wife critically injured.

He was taken to St George Hospital where he was in a critical condition on Saturday morning. His wife was taken to South East Regional Hospital, where she died from her injuries.

The police located the grandson and the car and launched a pursuit.

About 4.40pm, it's alleged the grandson tried to car-jack a second vehicle on Sapphire Coast Drive in the neighbouring town of Bournda, hitting a 55-year-old man on the head with a hammer.

The driver was taken to St George Hospital and remains in a critical condition. The female passenger was not hurt.

The alleged offender only managed to travel 500 metres before he crashed.

"He went into the bush to remain hidden," Chief Inspector Charman-Horton said.

"With a perimeter in place, and with assistance from further resources and specialists from around the state, ultimately he was located."

About 8.20pm, Police arrested the man and took him to South East Regional Hospital for assessment. He remains under police guard.

Asked whether any drugs were involved, Chief Inspector Charman-Horton remained tight-lipped, saying "he needed to go to hospital".

South Coast detectives, assisted by the State Crime Command’s Homicide Squad, are investigating the incident. Anyone with information should call Bega Police or Crime Stoppers on 1800 333 000.