Pakuranga murder trial witness describes the moment Chozyn Koroheke was shot dead

A witness has described the moment an Auckland mother was shot dead by her boyfriend.

Turiarangi Tai is on trial for murder after shooting 22-year-old Chozyn Koroheke in her Pakuranga home in April 2017.

But the defence says he should be found guilty of manslaughter, not murder.

Samantha Douglas, a housemate, said she was like a sister to Chozyn Koroheke.

She was in a relationship with Ms Koroheke's brother and was in the room when she was shot.

"He smacked her in the head with the shotgun, then he smacked her in the stomach with it - but pulled the trigger," she told the court.

Ms Douglas broke down in tears after telling the court what she'd seen, before describing how her shock and inability to respond.

"I sat there, I think what feels like a whole minute just going like this... I was hearing white noise, and I was just staring at her."

Ms Douglas said she then ran to a neighbour to call for an ambulance, While Mr Tai and Chozyn's brother Nacyn attempted CPR.

Earlier, she told the jury Ms Koroheke and Mr Tai would argue every day, describing the relationship as "rocky".

"They were both insecure," said Ms Douglas. "They would always think they were cheating, but I don't think either of them were."

She said Ms Koroheke had bruises on her face and arms caused by Mr Tai.

"Within the last month of her life, quite often," said Ms Douglas. "It got bad quick, you know - it wasn't always a horrible relationship."

In the week before Ms Koroheke died, Ms Douglas said Mr Tai hit her with a kitchen doorstop, prompting her to call an ambulance.

"He put a rock on her head," said Ms Douglas. "He smacked her with a rock."

The Crown says Mr Tai shot Chozyn Koroheke in anger, but his lawyers argue it was manslaughter.

The trial is set to last four weeks.