Rescuers have abandoned the search for 17 fishermen lost after a South Korean trawler sank in waters off Antarctica, saying there is no hope they survived a tragedy.

Five crew died immediately after the the 614-tonne Number One Insung, with 42 trawlermen aboard, went down in the remote area on Monday in an accident the boat's owners said may have been caused by an iceberg.

Twenty fishermen were rescued by another South Korean vessel.

'Unforgiving environment'

There were initial hopes some of the missing crew may have scrambled onto a lifeboat but they were dashed when three South Korean trawlers searched overnight and found no sign of the men.

The missing could not have endured 30 hours in the Southern Ocean without proper immersion suits, Maritime New Zealand said.

"Survival times for crew members in the water would be very short," Dave Wilson, rescue co-ordinator, said.

"The medical advice is that those who did not suffer cardiac arrest on entering the water would likely be unconscious after one hour, and unable to be resuscitated after two hours."

"Unfortunately, the Southern Ocean is an extremely unforgiving environment ... sadly, it is exceedingly unlikely that anyone not picked up yesterday could have survived," Wilson said.

The trawler sank at 6:30am, local time, on Monday (1730 GMT on Sunday), going down so quickly that Maritime NZ said it did not send an SOS and crew members had no chance to do protective gear in the rush to escape.

A coastguard spokesman in the South Korean port of Busan, where the ship is based, said there were eight Koreans, eight Chinese, 11 Indonesians, 11 Vietnamese, three Filipinos and one Russian on board.

The nationalities of the dead are not known.

Freezing conditions

The accident took place 1,000 nautical miles north of the McMurdo Antarctic base and 1,500 nautical miles from New Zealand's southern tip.

The Number One Insung was built in Japan in 1979, according to the website of the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR), the global body overseeing fishing in Antarctic waters.

The boat was not believed to have been ice strengthened for Antarctic waters, although immediate confirmation of this was unavailable.

Another South Korean trawler, the Oyang 70, sank in the Southern Ocean in August this year, with the loss of six lives. A New Zealand ship picked up 45 survivors.

'White gold'

Inquiries into that accident are continuing and New Zealand's Transport Accident Investigation Commission said it was ready to assist any probe into the latest sinking if requested by the South Korean Maritime Safety Tribunal.

"Because it's a Korean-flagged vessel and it occurred in international waters, it's their lead," commission spokesman Peter Northcote told AFP.

The stricken trawler was fishing for Patagonian toothfish, a rare species that lives in waters so cold that Greenpeace says it has a form of anti-freeze in its blood.

The fish, marketed as Chilean sea bass, is popular in South America, the US and Japan and is often illegally caught.

Greenpeace, which says the Patagonian toothfish is known as "white gold" in the industry for its highly valued flesh, lists it as a species in danger of being unsustainable.

Source: Agencies