A Northland schoolgirl was beaten repeatedly about the head, then dumped face down and unconscious to drown in a small creek, a High Court jury has been told.

Details of the final minutes of Kerikeri teenager Liberty Templeman's life were revealed yesterday during the first day of the trial of a 16-year-old accused of her killing.

The teen - whose identity is suppressed - faces a charge of murder and one charge of indecent assault.

He was 14 at the time of the alleged November 1, 2008, attack.

In his opening address, Crown prosecutor Mike Smith told the High Court at Whangarei Liberty had been hit about the head and knocked unconscious, then dragged and left face down in a creek on the outskirts of the town.

Her pants and underpants had been pulled down and her bra pulled up. She had bruises to both temples, nose, eyes and lips, the court heard.

Mr Smith said Liberty had recently moved from Kerikeri to Auckland and had returned to the town to spend a weekend with friends.

She had planned to catch a bus back to Auckland at midday on November 2, but by then others were frantically searching for her, he said.

"She would remain in that stream for nearly 24 hours until her body was discovered."

Mr Smith said Liberty had been at a barbecue in Kerikeri, not far from where her body was later found, and was expected to meet a friend when he finished work at 9pm.

Police learned Liberty was missing soon after as it was out of character for her not to let people know what she was doing. Mr Smith said there was an abrupt end to Liberty's text messages from about 6.30pm on the night she went missing.

The accused also stopped texting for about an hour during that time, the court heard.

When questioned by police, the boy repeatedly said he had last seen Liberty on the school field.

But Mr Smith said the boy returned home - meeting a curfew set by his parents - and put a shirt later found to have blood on it into a plastic bag, which was found buried in bushes near his home.

Mr Smith said that once the blood samples had been confirmed, the boy admitted in a later interview "to striking her, to strangling her, to putting her into the creek".

"He claimed that he pulled her clothes off and down ... to make it look like a rape, to make it look like someone else had hurt and killed this young girl."

The accused, wearing grey pants and a short-sleeved striped shirt, sat in the rear of the courtroom, flanked by court officials.

His parents, sitting just two metres behind him, shared his downcast look throughout the day's proceedings.

Justice Raynor Asher told the jury of six men and six women that they would hear some disturbing details about the "immensely sad death of a young person" throughout the trial.

Forty witnesses are expected to be called in the course of the trial, which is set down for at least two weeks.