A former Dilworth School student says he was chased by an alleged abuser after fleeing his house in the middle of the night.

The man, who cannot be named, has accused his former music teacher Leonard Cave of sexually abusing him at the teacher's bach on Waiheke Island in the mid-1980s.

Cave, 75, has pleaded not guilty to all charges against him, which relate to six complainants over several decades.

The former student, aged in his 50s, told the court that Cave had shown him pornography in his school office. On one occasion, he tore the pants off another student and took photographs of him, he said.

Later, he said he was invited to Cave's bach near Onetangi Beach, where the two of them drank beer and whisky at the property and a nearby pub.

In the evening, Cave initiated a game which involved removing items of clothing, the complainant told the court.

"I was moderately inebriated. He moved forward, started touching me, performed oral sex on me. I was just stunned."

Cave then led him into a bedroom and asked for sex, he said.

"I had a moment of clarity: 'Oh my God what's going on here?'."

The man said after re-dressing he ran to the back door of the house, while the teacher called after him. He ran down the street towards Onetangi Beach.

"I was going, 'I've got to get out of here, get away from this guy'. I was walking pretty fast, heading back down towards the beach at Onetangi. I'd heard these footsteps behind me."

The man said he turned and saw Mr Cave running towards him, clothed but barefoot. He ran to the pub where they had been earlier in the nigh and asked the staff to call a taxi.

"I remember the [barman] saying to me 'Are you all right?'"

While he was waiting outside the pub for the taxi to arrive, he saw Cave searching for him.

The taxi took him to a friend's place in Little Oneroa, where he told them what had happened. His mother later laid a complaint at Dilworth School.

Cave left the school soon after the incident. The court heard that the complaint was never referred to police.

Defence lawyer Warren Pyke challenged the former student, saying that the alleged sexual abuse never occurred, and that he was not chased by Cave.

"The incident occurred as I described," the man said.

The trial is expected to wrap up next week.