The majority of oily waste from last night's spill into Tauranga Harbour has been recovered, and revealed to be mainly cooking oil.

An estimated 2000 litres of oily sludge is believed to have been discharged from a tanker truck about 5pm Monday as it was removing the sludge from a vessel at Sulphur Point. Some of this sludge entered the water.

Bay of Plenty Regional Council staff worked into the night to clean up the mess, using booms and other spill equipment. The work was halted late on Monday and resumed at first light on Tuesday.

The council said the spill was mainly made up of cooking oil mixed with residual bilge oil.

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This was after a vegetable oil bladder on board the vessel spilled to the vessel bilge.

Vegetable oil would rapidly disperse in this environment, however, some avian wildlife may still be affected.

Regional on-scene commander Adrian Heays said staff worked through to 11pm to contain and recover the oil.

"Maritime and compliance staff were on the scene quickly after the spill was reported just after 5pm last night.

"Using a combination of sorbent booms, our harbourmaster vessel, Awanui, and its onboard skimmer, as well as two small vessels chasing fugitive oil, it appears the majority of the oil has been recovered."

Staff had been at the scene earlier on Monday when a smaller spill occurred involving the same vessel and tanker truck. It was believed around 60 litres was spilled then, with around 10-20 litres going into the water.

The cause of the incidents is not thought to be related. A full investigation has begun into both.

Heays said it was fortunate the booms had remained in place after the smaller spill, which helped contain some of the oil from the later spill before it could travel further into the harbour.

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On Tuesday staff were focusing on an environmental and wildlife assessment both on and off-site, monitoring, clean up and equipment replenishment.

"Because of Covid-19 we are applying PPE and distancing requirements as stringently as possible, and have worked to streamline our response as much as we are able," Heays said.