Six crew were still missing after a New Zealand chartered foreign fishing boat sank in the Southern Ocean early Wednesday morning.

Forty-five people have been rescued from life rafts following the sinking of a Korean company owned trawler, Oyang 70, in the Southern Ocean Wednesday morning, Radio New Zealand reported.

The New Zealand Rescue Coordination Center received an alert from the the 82-meter trawler at 4:40 a.m. on Wednesday, about 400 nautical miles (740 km) east of New Zealand southern city of Dunedin.

That was followed shortly after by a mayday call from the same position, relayed by fishing vessel Almatal Atlantis, reporting that the Oyang 70 had sunk.

Seven fishing vessels, including the Almatal Atlantis, were at the scene and searching for the remainder of the crew, the Rescue Coordination Center said.

Weather in the area was good, but foggy and extremely cold. The 45 rescued crew were on board the Almatal Atlantis and the search was continuing for the six missing people.

The cause of the sinking was not yet known. The 82-meter-long Oyang 70 is believed to be a fishing factory ship with a displacement of about 1,500 tonnes.

The Royal New Zealand Airforce has deployed an Orion surveillance aircraft to help with the search.