The dramatic moment a man was allegedly stabbed in the heart by a teenage girl has been revealed to a jury at a High Court murder trial in Hamilton.

The fateful confrontation was recounted on Monday at the trial, where a 16-year-old and a 14-year-old each stand accused of murdering Norman Kingi, 54, who died following the incident in Rānui Street in Dinsdale, Hamilton, about 11.30pm on Friday, July 28 last year.

The Crown case against the pair alleges they were the elder two of three girls - at the time aged 15, 13 and 12 - who were caught in the act of breaking into a Nissan Primera owned by Kingi and his partner Vicki-Lee Reihana. The vehicle was parked on the roadside outside their house.

The couple happened to be walking home from the Frankton Railways Combined Sports Club at that time and, seeing that their car was being invaded, ran to stop the trio. The 12-year-old was caught by the woman and held at the scene. The other two ran off as Kingi rang police.

But, as Crown prosecutor Philip Morgan, QC, told the trial's jury, "they decided to return to rescue [the 12-year-old]" after first arming themselves with a knife and a screwdriver.

Giving evidence, Reihana said she and Kingi had seen the interior light on in the car as they approached. She had grabbed the girl who was too slow to get away, restraining her by holding her against the car door.

"She was just screaming and thrashing ... I told her to shut her mouth."

Reihana said she heard the other girls shouting as they returned.

They were yelling: "Let her go or we'll f...ing do you."

As they approached Kingi, "the tall one threw a punch and I thought it was just a punch."

She had not realised the older girl was holding a knife.

"The little girl I was holding just started screaming and screaming and I turned to look at her ... when I looked around, Norman was on the ground."

Kingi "was just gargling" when she ran to his side. The girls ran from the scene while Reihana began screaming for help. Neighbours ran to her aid and a short time later, an ambulance and the police arrived.

Efforts were made to save Kingi's life, but to no avail.

Morgan told the jurors they would hear that once she was apprehended by the police later that evening, the older girl was found to have blood on her clothing.

Later DNA testing of that blood found it to be Kingi's, and the jury will hear evidence about that later in the trial, Morgan said.

Due to their young age, the two accused have interim name suppression until the conclusion of the trial, at which point a final decision will be made on whether they can be named.

Hamilton lawyer Roger Laybourn is acting for the 14-year-old, while Auckland lawyer Ron Mansfield is counsel for the 16-year-old.

In his opening statement, Mansfield said his client was acting instinctively against Kingi's advances on her.

"She was responding to an event that was unexpected ... She was acting instinctively to defend herself and she certainly did not have any intention to kill or seriously injure Mr Kingi."

Laybourn said his client should not have been charged with murder by the police.

"When the evidence unfolds, there is nothing that she did that could make her a party to a joint action ... where death was a consequence."

The Crown case is being handled by Morgan with assistance from Shelley Gilbert.

The Crown intends to call 32 witnesses.

The trial, before Justice Timothy Brewer, began on Monday morning with the empanelling of the jury of seven women and five men, followed by some opening remarks by the judge. It is estimated to run for two weeks.

The two defendants have the help of communications assistants in the courtroom for the duration of the trial. Their role is to ensure the defendants are following and understanding what is happening. The court is also adjourning early in deference to the defendants' age.

-Stuff/Mike Mather