Six people were rescued by a passing ferry in Foveaux Strait on Tuesday morning after their fishing boat sank 50 nautical miles off the coast from Bluff.
The Stewart Island ferry responded to a mayday call about midday, and picked up the group soon afterwards.
Police say overloading and incorrect weight distribution probably caused the six-metre fishing boat to sink as it headed out from Bluff.
Constable Nick Wells of the Stewart Island police says the boat has been recovered and the survivors are now out recovering fishing and diving gear that had floated away.
The six men were rescued from a small inflatable near the Muttonbird Islands.
The men managed to get into the inflatable and raise the alarm as their six-metre fishing boat was sinking, and were picked up 15 minutes later.
All were wearing lifejackets and had the right safety gear, but police in Stewart Island say the boat may have had too much diving and fishing gear loaded aboard.
The fishing boat is being examined.