Two swimmers struggled in vain to save the life of a man who got into difficulty during a cross-harbour swimming race in Auckland yesterday.

The man, believed to be in his late 50s, was plucked from the water by rescuers after swimmers found him face down in the water, but was later pronounced dead. He was competing in the sixth annual Sovereign Harbour Crossing, part of the New Zealand Ocean Swim series.

The death is the fourth in the Ocean Swim series, following a death in the Harbour Crossing in 2005, and deaths in the King of the Bays event in 2007 and 2008.

Auckland police said a post-mortem examination would be held today or tomorrow to determine the cause of death.

As surf life saving staff last night comforted the three volunteers directly involved in the rescue attempt, one official said there had been "too many people dying" in swimming races worldwide.

Surf Life Saving New Zealand chief executive Jeff Barry also said New Zealand has had its "fair share".

Surf Life Saving guards patrolling yesterday's 2.8km race between Bayswater and the Viaduct noticed two swimmers trying to support the man early in the race.

The lifesavers, patrolling on surfboards, immediately whistled for a rescue boat, which took the man and the other two swimmers to shore.

They were attended by St John Ambulance staff but the man could not be revived.

The race organisers had a full health and safety plan in place, with about 30 lifeguards and inflatable boats in the water during the race. "I think we had it pretty well covered," said Barry. "At the moment we are dealing with lifeguards who are dealing with death for the first time."

Event director Scott Rice last night refused to tell the Herald on Sunday what specific safety measures were in place before the swim. A debrief would be held this week and the event would be reviewed. St John Ambulance and Surf Life Saving staff would attend the meeting.

Barry said his organisation had been directly associated with the series for three years. He agreed with the need to review the number of incidents of people dying during swimming races, he said.

"People are more at risk in the water than if they are doing a fun run or a bike race. I guess in a fun run you can stop and walk though."

Emergency doctor John Bonning, who has competed in endurance mountain bike events, said preparation for competitive events was the key. "Fifty years old - if you hadn't trained it is asking the body to do a hell of a lot. In a swimming event, clearly you can't just hop off your bike."

Conditions for entrants on the Ocean Series website include a requirement for swimmers to undertake "appropriate training" and have a medical check.

The website adds that the events are "demanding."

"Possible risks include drowning, being hit by a boat, object or person, shark attack or marine stinger."