Kristy Duley told a Newcastle Supreme Court jury on Tuesday her half-brother, Justin Fuller, was armed with two large knives when he attacked Guy McCulloch, her partner of 26 years and father to six of her seven children.

Mr McCulloch had been in the driver's seat of the couple's black Nissan Navara with Ms Duley sitting beside him in Beach Street, Belmont South, in December 2018 when Fuller lunged at him through the window.

"He (Fuller) f***ing kept stabbing and stabbing him with knives bigger than my arms," Ms Duley said.

"He (Mr McCulloch) was trapped in his seat belt. He was dying in front of me.

"I couldn't stop the blood. It kept pouring through my fingers."

Fuller, 34, has pleaded not guilty to murder but guilty to the lesser charge of manslaughter.

Crown prosecutor John Stanhope had earlier told the court Fuller was armed with two 45cm-long machetes when he leaned into the driver's side window and stabbed Mr McCulloch four times.

Mr McCulloch, 50, bled to death after one deep stab wound penetrated his liver.

Mr Stanhope said there was no issue Fuller had killed Mr McCulloch, who went by the nickname "Wink", but the jury had to decide if he had intended to kill him or cause serious injury.

Defence barrister Winston Terracini SC told the jury the trial would also look at issues involving self-defence and provocation.

Mr Terracini said there had been a longstanding, toxic relationship between Fuller and Ms Duley, with the animosity extending to Facebook messages where she expressed feelings of hatred for her half-brother.

The defence barrister claimed Ms Duley had also posted Facebook messages declaring it would be a great birthday present or Mother's Day gift if their mother was bitten and killed by a brown snake.

In his opening address to the jury, Mr Stanhope said the fatal stabbing took place after Fuller had been a passenger in a silver Holden Commodore driven by his then girlfriend, Narelle Abercrombie, when they passed Ms Duley and Mr McCulloch parked in Beach Street talking to friends.

Ms Duley called out "Tick Tock" to Ms Abercrombie and she gave Ms Duley the finger.

Fuller later approached Mr McCulloch's black Nissan Navara on foot and argued with his sister and her de facto before Mr McCulloch twice reversed his car into Ms Abercrombie's Holden Commodore, stopped directly behind him.

Mr Stanhope said Fuller then went to his home nearby and grabbed a backpack with two large knives before walking back to the Navara where Mr McCulloch and Ms Duley were still seated inside.

As Fuller approached, one of Mr McCulloch's friends saw him and called out: "He's got knives, go."

But before Mr McCulloch could drive away, Fuller reached through the driver's side window and stabbed him with the machetes.

The trial continues.

Australian Associated Press