Hope was fading last night for 17 missing fishermen after their South Korean trawler In Sung sank in the Southern Ocean, claiming at least five lives.
The boat sank in international waters but was in New Zealand's search and rescue region, meaning the Rescue Co-ordination Centre New Zealand (RCCNZ) controlled the search operation.
Two New Zealand fishing boats - from seafood company Sealord - assisted with the rescue bid for the 42 sailors.
Last night five of the sailors had died and their bodies had been recovered, 20 were rescued and 17 were still missing. But rescuers' hopes were fading for the missing men who would not have survived more than 10 minutes in the water.
RCCNZ search and rescue controller Dave Wilson said it was not known what caused the vessel to sink or why no distress communication was received before it went down.
The rescue vessel and fishing company said the boat sank quickly and those able to abandon ship did so directly into the water without life jackets or immersion suits.
"At the moment everyone is focusing on saving as many people as possible and finding all those people who are missing.
"Causes can be worked out afterward," said a RCCNZ spokesman.
The 58m long-liner sank about 6.30am yesterday morning, 2700km southeast of Bluff. Eight South Koreans, eight Chinese, 11 Indonesians, 11 Vietnamese, three Filipinos and one Russian were on board.
The dead included two Indonesians, one South Korean and one Vietnamese, a Foreign Ministry official said.
The 20 survivors and five deceased were last night on board the Korean fishing vessel No 707 Hongjin.
A Royal New Zealand Air Force Orion was considered to help with the search at one point, but it would take at least eight hours to get to the area from the time it left New Zealand.
"Unfortunately, given the short survival times in water of those temperatures and the length of time it would take for the Orion and Hercules aircraft to reach the search area, it was not a viable option," Mr Wilson said.
Weather conditions in the area were decent with a light westerly at 10 knots and a 1m swell.
Coastguard New Zealand chief of operations Richard Bray said the rescue was a category two.
"That's our highest and most serious alert for search and rescue operations.
"It means it's very serious."
This is the second time this year a Korean fishing vessel has sunk quickly resulting in deaths in waters near New Zealand.
In August, six men died and 45 were rescued after their vessel sank in just 15 minutes in calm waters 400 nautical miles from Dunedin.
