A woman who's accused a Northland police officer of sexually assaulting her while investigating crimes against her says the experience was a "nightmare".

Detective inspector Kevin Burke, who was based mostly in Orewa, is on trial at the High Court in Auckland on two charges of indecently assaulting a woman over 16, and two of unlawful sexual connection.

The complainant, whose name and voice are suppressed, said she met with Mr Burke in 2002 to discuss her worries about a man's fraudulent behaviour.

Under examination by Crown Prosecutor Jo Murdoch, the woman said the detective told her she had been trying to find this particular man for a long time.

"The fact that somebody believed me, I just felt so fantastic that it wasn't just a figment of my imagination," she said.

About two weeks later he turned up to the first complainants house unannounced with a box of beer and a wine bottle.

The complainant said she thought that was strange.

He started to talk about the investigation and drink about 12 bottles of beer that he brought to her home, she said.

"I kept thinking, god he can drink and I remember thinking he's got to drive, how is he going to drive after drinking so much?" said the complainant.

She gave him some pasta and made up a bed for him in the spare room to stop him from driving intoxicated.

The woman said when she was pointing out the room to Mr Burke, he grabbed her, and pulled her on top of him onto the bed and she struggled to free herself.

She alleged Mr Burke pushed her off the bed onto the floor and held her arms above her head with one hand and partially pulled down her leggings before sexually assaulting her.

"I just thought what the hell, how did it get to this?" said the complainant.

"What on earth just happened? I just kept thinking this was like a nightmare."

She became emotional as she recalled how she said she tried to get away from the detective.

"He just seemed so angry, just quite aggressive."

She said other than a few swear words, he did not say anything else during the entire incident.

The complainant claimed that Mr Burke pulled her back onto the bed, fell asleep and she found him gone the next morning.

The woman said she never saw the detective again and he never contacted her again about the fraudster.

She did not report the matter to police at the time.

"Who would have believed me? Who would I have told?", she said.

It was only after she saw another woman had laid a complaint against Mr Burke for sexual assault in 2017 that she decided to also lay a complaint.

The complainant will be cross-examined tomorrow by the defence.

The defence has said in its opening statement that the sexual activity was consensual.

A second woman is also accusing Mr Burke of sexually assaulting her and will give evidence later in the trial.