The man found dead at a Christmas party on a luxury yacht in Auckland's Viaduct died of asphyxiation, say police.

The death of Darren Perry Grace is being investigated as a homicide.

Detective Senior Sergeant Kevin Hooper said Mr Grace was a guest on the yacht. He said other guests were helping police with their inquiries.

Yesterday, police denied media reports the 40-year-old Auckland builder's death was suspicious.

"My position is that it's explained, there's a big difference really," Mr Hooper said.

Yesterday he refused to speculate on cause of death and said police were awaiting results of the post mortem examination and other medical tests.

But there was no suggestion Mr Grace had taken any illicit substances, he said.

"Once we've got cause of death we'll take it from there."

About 40 people were on board the Quest II luxury yacht on Friday night for company Pacific Hygiene's Christmas function. It is understood Mr Grace was a friend of a staff member.

Company director Rodney Downs could not be reached for comment yesterday but told the Herald on Sunday there had been desperate efforts to save Mr Grace's life.

"It was a terrible tragedy. We don't know the cause of death but everyone is shattered," he said.

Mr Downs said the party had been under way for about 90 minutes when Mr Grace started acting "a bit funny".

The yacht's skipper was worried about him and tried to calm him. Moments after he sat down in the lounge upstairs he collapsed.

Mr Hooper confirmed the builder's body lay next to a drink table between two couches, on the flying deck.

He said all 40 people who attended the party were co-operating with police and no one else was being sought.

"We are working our way through speaking to them," Mr Hooper said.

Over the weekend, forensic experts combed the vessel, while detectives conducted inquiries and fingerprints and photographs were taken.

Last night, Mr Grace's family were making arrangements for his funeral.

- with NZ HERALD STAFF