"A diver has just arrived at the scene and will be going underwater this afternoon to block the breathers of the fuel tanks to stem the flow of diesel," Mr Lovatt said.
"There's an estimated 200 litres of diesel on board, but at the moment only tiny amounts is escaping into the water. We have our harbourmaster on the scene monitoring the situation and we have booms on standby ready to be deployed if required.
"However, the good news is that the choppy conditions will help to disperse and break up the diesel and minimise any environmental impact," Mr Lovatt says.
As a precaution, iwi and nearby shellfish farmers have been notified of the incident.
The owner is liaising with an Auckland-based salvage company to arrange removal of the sunken vessel from the water, which may take a few days.