"The vessel is listing but remains secured to its mooring, with approximately 500 litres of diesel fuel on board, which is leaking into the water," the council said in a statement.
Regional on-scene commander Derek Hartley said the council was considering mobilising its marine oil-spill equipment, but weather conditions at the moment would prevent the deployment of booms to contain the diesel.
"We have our Whangamatā-based harbourmaster closely monitoring the situation from the shore," Hartley said.
"Unfortunately it's just not safe to go out on the water at this time, with the conditions making it impossible for us to assess just how much of the diesel is spilling from the vessel into the water."
But he said the good news was that the vessel hasn't sunk yet.
"Due to the volatile nature of the diesel, wind and tide conditions, the fuel is likely to disperse well with minimal ecological impact," Hartley said.
Hartley said salvors are due to arrive at the scene tomorrow, when the weather is expected to improve and enable safe salvage of the vessel.
In the other incident, the yacht is resting on rocks above the high tide line in Flaxmill Bay and has no fuel onboard.
The council's Whitianga harbourmaster is at the scene and anticipated there will be minimal environmental impact.
Salvage experts, who have arrived on scene, are working on recovering the vessel and getting it to the Whitianga marina.
