SEARCH UNDERWAY: The boat Easy Rider was heading north near Stewart Island when it capsized with nine people on board.

A rogue wave caused a fishing boat to capsize in Foveaux Strait with nine people on board, the only known survivor of the tragedy has told police.

Easy Rider, a 38-foot vessel, capsized off Saddle Point at the northern tip of Stewart Island, in 13degC waters well known for rips, about midnight Wednesday.

Two months ago the boat had been involved in a heroic rescue in the same treacherous waters.

Fairfax NZ LOST AT SEA: Easy Rider, a 38-foot vessel, capsized off Saddle Point at the northern tip of Stewart Island at about midnight on Wednesday.

Newstips: Do you know anyone who was on the Easy Rider?

EASY RIDER SKIPPER: Rewai Karetai.

One person has survived 18 hours in the chill waters of Foveaux Strait, but hopes have faded for up to seven others - two young children among them - missing after a Southland fishing boat went down in treacherous waters.

One body, believed to be that of an eight-year-old boy, has been found.

The survivor was found at 6pm tonight, four hours after the alarm was raised, and 18 hours after the sinking.

Easy Rider was heading north near Stewart Island when it capsized around midnight, Inspector John Doherty said.

The alarm was raised 14 hours after the capsize, when Easy Rider failed to make a 2pm rendezvous at Stewart Island.

Police said the survivor was on the deck of the boat with two others when it was hit by a rogue wave, which caused the boat to capsize almost immediately.

The rest of the passengers were said to be in the wheel house of the boat.



The survivor was able to pull himself up onto the hull where he remained for approximately two hours before the boat sank.

Easy Rider skipper Rewai Karetai, hailed as a hero for a rescue in the strait two months ago, was understood to have been on board.

A full search for the missing passengers and crew will resume at 6.30am, after it was scaled down about midnight, police said.

Family member Jill Karetai said the nine people on board the boat were mostly members of the wider Karetai whanau.

"They were on their way to the Mutton Bird Islands and left about 6pm last night. Rewai Karetai is my nephew. He was definitely on the boat when it left last night. We are all in a state of shock at the moment ,'' she said.

Karetai regularly sailed to the islands at this time of the year. "He drops people off for months at a time down there," she said.

Whanau had told her the missing family members, aged from in their 60s to children, had left on the Easy Rider "all cheerful last night''.

They were from all over Southland and were the first batch of the family to go to the islands for the season.

The Maori community in Invercargill, including family members, a priest and Maori social workers had visited her during the evening, Jill Karetai said.

"We are just living in hope and waiting, it's like being suspended in ice. It's like a horror movie ... it hasn't sunk in.''

Also on board was 29-year-old Shane Topi, who worked with Mr Karetai.



Shane Topi's mother Helen Topi said police told her yesterday afternoon that Shane was on the Easy Rider and it wasn't good.



She said her son hated the water.



In 2006, Shane's cousin Peter Topi died when the Kotuku sank in Foveaux Strait, killing six, including several members of the Topi family.



Shane's flatmate, Adam Swatton, said Shane could not swim. He described his mate as a big solid guy with a heart of gold.



"He kept his friends close and his family closer," he said.

The Easy Rider was involved in a rescue operation of another fishing vessel in January, and Mr Karetai was hailed as a hero.

Two of the five people on board the fishing boat died after it capsized near White Island.

Easy Rider spotted the three survivors and rescued them, with Mr Karetai hailed as a hero after he battled heavy seas, tidal currents and high winds to pluck three people to safety.

Barry Bethune, who was rescued by Mr Karetai in January, said he'd been receiving calls from friends and family after the Easy Rider was identified.

Mr Bethune said it was hard to hold on to hope, knowing the conditions of the strait.

"Knowing that Rewai...''

"I'm just bloody devastated ... this has brought everything back.''

A MetService spokesman said there was heavy rain and gale force winds in Foveaux Strait at the time the boat capsized.

There was also four metre swell on the open ocean.

"The sea was probably very rough.''

The wind turned southwest and dropped overnight.

The water temperature in Foveaux Strait was currently 13degC. In water temperatures between 10 and 16degC, a human's expected survival time was between one and six hours.

A person would usually lapse into unconsciousness in between one and two hours.

Cold water robs the body's heat 32 times faster than cold air.

Southland area commander Inspector Lane Todd refused to comment but said police would be sending out regular updates.

A media conference was expected to be held mid-morning tomorrow.

After the January rescue, Mr Karetai said Maritime New Zealand should educate recreational boaties more on how to keep safe on the water.

Little things such as putting cellphones into zip-locked plastic bags were essential, he said.

It is the second major sea incident involving a muttonbirding family in Foveaux Strait.

In May 2006, fishing trawler Kotuku sank while returning from the Muttonbird Islands after being struck by two rogue waves.

Six of the nine people on board died - 52-year-old Ian Hayward, nine-year-old cousins Shain Topi-Tairi and Sailor Trow-Topi, the children's grandfather, Leslie (Peter) Topi, 78, Sailor's mother, Tania Topi, 41, and Clinton Woods, 34.

Three people, skipper John Edminstin, Paul Topi, and Dylan Topi, survived the ordeal after swimming about 500m through heavy seas to Womens Island. Woods also swam to the island but died before he could be rescued.