Police have released the name of the fishing vessel they are searching for off Fiordland.
The K'Cee is believed to have sunk near Secretary Island at the mouth of Doubtful Sound.
It is a 10 metre aluminium crayfish boat.
Invercargill police Inspector Lane Todd says police understand there are two people on board but are yet to confirm their names.
"We've currently got police family liaison with the families involved and we're obviously seeking information from them at the moment, with their ongoing enquiries, and they're obviously quite distressed."
Lane Todd says a small amount of wreckage has been found near Secretary Island but any connection to the missing boat hasn't been confirmed.
Inspector Lane Todd says a member of the public alerted police just after 10am.
K'Cee Skipper Bruce Gordon plucked a group of 8 people off the rocks in Doubtful Sound after their catamaran sank in poor weather in March
Bluff Fishermen's Radio operator Meri Leask says his boat is based in Doubtful Sound.
"He fishes the Fiordland coast, Doubtful Sound, Milford Sound through that area. As I understand he crayfishes in that area all year round."
Police haven't confirmed whether Bruce Gordon is onboard this missing boat or not.
The boat is believed to have sunk off the west coast of Secretary Island at the mouth of Doubtful Sound
Environment Southland on scene commander Dallas Bradley says he's liasing with Department of Conservation's wildlife experts about the threat that any diesel spill would pose.
Bradley says Secretary Island is a very sensitive area where DOC had eradicated predators to make a sanctuary for endangered birds. He says the missing boat could have up to 5000 litres onboard.
So far there have been no reports of any oil slicks.
Photo: Doubtful Sound (APN)