A Whangarei man is on trial charged with sexually abusing two women who have severe intellectual impairments.

David Dennis Karanga Wira has pleaded not guilty to 11 charges alleging he committed indecencies against the two women in September 2014.

Wira is on trial in the High Court at Whangarei before Justice Timothy Brewer and a jury of seven women and five men.

He is charged with two counts of rape, one of sexual violation by unlawful sexual connection, one of attempted sexual violation and three of indecent assault against a woman in her 20s between September 16 and 18, 2014. He is facing one charge of sexual violation by unlawful sexual connection and three of indecent assault against a woman in her 50s on September 4, 2014.

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Crown prosecutor Nicole Dore said Wira approached the older woman in Onerahi on September 4, 2014 and forced her down an alley where he committed the indecencies.

Ms Dore said Wira went into the younger woman's flat in Whangarei between September 16 and 18, 2014, and committed the indecencies, including two rapes.

She said DNA evidence to the court would show that semen stains found on the clothing of both women showed it was up 10 million times more likely that to have come from Wira than anybody else in New Zealand.

"The experts will say that is extremely strong scientific support that [the DNA] came from Wira," Ms Dore said.

She said both women were classed as having very low IQs and severe intellectual impairments and they did not consent to the acts.

Ms Dore said the Crown would prove the case against Wira beyond reasonable doubt.

In a brief opening statement to the jury defence lawyer Sumudu Thode said Wira acknowledged there was interaction with both women, but not in the way that they have described it.

"The defence says that what they say and the way that they say these incidents happened simply didn't happen. When you have heard all the evidence you will be sure that their stories are simply not plausible," Mrs Thode said.

The case is set to last two weeks.