A 30-metre fishing boat, filled with 50 tonnes of salmon, has sunk at the Eden wharf on the NSW Far South Coast.
Fire and Rescue NSW were called to reports of a partially submerged boat around 3:30am, which was discovered by the captain and crew.
Inspector Phil Eberle said 50 tonnes of salmon on board was secured into the hull prior to the vessel completely sinking about 30 minutes later.
"The crews have got in quickly, and organised the captain and deckhand to secure the hatches before it went under," he said.
"We didn't have fish floating all through the harbour."
Fire and Rescue NSW says firefighters worked with the owner to try to secure the vessel, but it was taking on too much water and sank.
Mr Eberle said no-one was on board the boat or sustained any injuries when it sank.
Booms deployed
Emergency services are still at the scene, including police, monitoring a slow diesel leak coming out of the vessel.
Fire and Rescue NSW crews have deployed absorbent oil booms into the water with the assistance of the harbour master.
"But at this stage, there doesn't appear to be any that has hugely escaped the vessel."
The ABC understands the boat was operated by locals, which transports salmon to South Australia.
The cause of the sinking is not yet known.
"At this stage, we haven't really investigated as to why it's sunk, but unfortunately it has," Mr Eberle said.
"For a bad situation for the poor [fisher] and his business, we've got a good situation where we've managed to look after the environment."
A plan to salvage the boat is still being formed.