One fisherman drowned yesterday and three others spent almost eight hours clinging to their upturned boat after it capsized in the mouth of the Manukau Harbour.

Coastguard search and rescue controller John Cowan said the quartet's 5m red aluminium runabout ran into trouble about 8am. It is understood some of those on board were prison officers.

"They were heading out across the bar and it was quite rough. They tried to turn around, and as they were doing that, the boat overturned."

Cowan said two men were thrown into the water. The other two were forced into the boat's cabin. Only one of the trapped pair managed to make it out. The trio clung to the hull of the overturned boat for almost eight hours and were only rescued after someone on shore noticed the wreck.

The Coastguard was notified at 3.40pm, and two boats and an aircraft were used to search the region.

Cowan said the troubled boat did not have waterproof communications equipment and the men had not notified the Coastguard of their outing. "They were really lucky someone spotted them from the shore."

The survivors were pulled from the water shortly before 4pm and taken to Whatipu. They were then flown by helicopter to Waitakere Hospital.

Westpac Rescue Helicopter crewman Leon Ford said two required medical attention for exhaustion and hypothermia. They were last night in a stable condition in hospital.

A body was recovered as the Coastguard attempted to right the vessel. Police said the dead man was a Maori aged about 50. It was unclear if he was wearing a lifejacket.

Ford said the survivors - who were wearing lifejackets - didn't speak much during their flight to hospital.

"Not a lot, they were pretty cold - they'd been in the water since 8am."

One witness to the salvage operation said the area was dangerous for boaties.

"So many people have died since I've been here. They die all the time. Manukau Harbour is really dangerous and people go out in tiny little boats."

In March 2005 a man drowned and two others were injured when their fishing boat was swamped on the Manukau bar.

The region is also the scene of the worst shipwreck in New Zealand history when 189 people drowned after the HMS Orpheus sank in 1863.

Cowan said the stretch of water had been more treacherous than usual over the past week.

Cowan said there were lessons to learn from the tragedy.

Boaties should always ensure they have a way of raising the alarm if they run into trouble by carrying a waterproof VHF radio or a cellphone in a snaplock bag.