A salvage operation is underway to retrieve a stricken vessel leaking diesel into the Whangamatā Harbour.

The Waikato Regional Council received reports around 8am yesterday of a commercial longliner taking on water in the Whangamatā Harbour and notified its regional on-scene commander.

Regional on-scene commander Derek Hartley said conditions on the harbour this morning were much improved and had enabled crews to travel to the vessel to undertake salvage operations.

"There's good news this morning. Preliminary investigations suggest there has not been a significant amount of diesel discharged into the environment, which means the ecological impact is likely to be minimal," Hartley said.

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"Salvors are on board the long liner and they have already carefully removed the water on board the boat, ensuring there was no discharge of diesel."

Yesterday, Coastguard traveled to the vessel and attempted to right it, but their efforts were stopped by significant wind and extremely choppy on water conditions.

The crew was forced to return to shore.

The vessel remained secured to its mooring with approximately 500 litres of diesel fuel onboard, which was leaking into the water.

Yesterday, Hartley said the council was considering mobilising its marine oil spill equipment, but weather conditions would of prevented the deployment of booms to contain the diesel.

"We have our Whangamatā-based harbourmaster closely monitoring the situation from the shore. 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."

He said it was good news that the vessel had not sunk and due to the nature of the tide and diesel, it was likely to disperse well with minimal ecologic impact.