Lynace Parakuka was in the first trimester of pregnancy when Jason Wiremu Poihipi attacked and savagely beat her to death, a jury in the High Court at Rotorua has heard.

They are trying Poihipi, 19, for the murder of Parakuka, his 22-year-old partner, in the grounds of Rotorua's St Michael's Catholic School in the early hours of September 7 last year.

When the trial opened this morning Poihipi denied the charge.

Opening the Crown's case prosecutor Duncan McWilliam described how Poihipi had told police he attacked Parakuka because he was in a jealous rage, ignited by seeing her through a window having sex with another man.

He outlined how Poihipi confessed to slamming her in the face four or five times until she fell to the ground where he kicked her, again the blows were to her face and head.

However a pathologist would testify Parakuka had suffered between 11 and 20 separate blows which resulted in bleeding to the brain, the cause of her death.

McWilliam told the 10 women and two men on the jury that Poihipi sat on the ground beside Parakuka listening to her increasingly laboured breathing before running to his cousin's house where he told her he had given Lynace a hiding.

Paramedics arrived soon after the cousin dialled 111 but had been unable to revive Parakuka.

McWilliam claimed Poihipi gave police varying versions of what happened. In one he said he found her on Clayton Rd with black eyes and a bloodied nose. She told him she'd been attacked by a group of girls, that they'd walked into the school grounds where she collapsed.

He told another constable his "missus" had taken off. When he found her injured she said "the n******s did this to me".

McWilliam said it was apparent Poihipi had lied in subsequent interviews, including one recorded on DVD which the jury would see later in the week.

"This is not a who done it," McWilliam said. "This is a murder caused by the number of blows inflicted by the defendant and the severity of them . . . There were multiple acts of violence while he was overwhelmed with jealousy."

In his opening statement, Poihipi's lawyer Roger Gowing said a tragic turn of events had left Parakuka dead and Poihipi was responsible for her death because he assaulted her, that she had died as a result of the injuries she received.

Lynace Parakuka was in the first trimester of pregnancy. (Photo / Supplied)

"It is trite to say he has to live with the loss of his partner for the rest of his life, that is the fact of the matter, but the issue you will need to concentrate on in this trial is did he know what he did was likely to cause her death? Was he reckless in carrying out the assaults and what was in his mind at the time he assaulted her?" he submitted.

It was the defence's contention Poihipi was guilty of Parakuka's manslaughter not the murder he is charged with.

As Justice Ian Gault was outlining to the jury how the trial would run a man entered the court yelling to Poihipi "love you bro". A security officer removed him.

She was found dead at Rotorua's St Michael's Catholic School in the early hours of September 7 last year. (Photo / Supplied)

Throughout the Crown's opening, several women in the public gallery sobbed, passing a box of tissues between them as Poihipi sat impassively in the dock.

It's anticipated the trial will run until Friday.