Mobil estimates about 1500 litres of fuel has been leaked into Tauranga Harbour this week and the oil has now reached Pilot Bay.
The fuel oil leaked into the harbour on Monday during a ship bunkering operation, from two corrosion holes about 4mm wide in a 150mm wide lateral pipeline.
Mobil Oil New Zealand Country Manager Andrew McNaught said, "While it is difficult to make an accurate assessment of the volume lost given the circumstances, Mobil estimates the volume of fuel leaked into the Harbour to be approximately 1500 litres."
"The pipeline system to the wharf has been shut down until inspections and testing can be done on all sections of the pipeline branches along the wharf to ensure their ongoing integrity.
"The investigation is continuing and the priority is to understand how this failure occurred. Further metallurgical testing of the pipe will be required to understand the specific cause, and this will take some weeks," he said.
Bay of Plenty Regional Council On Scene Commander Jim Tetlow said it had received reports of oil at the popular Mount Maunganui beach.
Read more: Oil spill: 'The volume is irrelevant' - Mobil
A crew was this afternoon at Pilot Bay in effort to clean it up, Mr Tetlow said.
The Pilot Bay clean up follows an update earlier today from the regional council stating it had already collected 12 tonnes of oil and oil waste.
A clean-up crew of about 70 people worked yesterday to clean up oil at Maungatapu and Bridge Marina and shoreline assessments continued. The workers included staff from Bay of Plenty Regional Council and Tauranga City Council, Ministry for Primary Industries fisheries officers, Envirowaste, trained oil responders from Waikato Regional Council and volunteers from local iwi/hapu and the community.
An unknown amount of oil had leaked into Tauranga Harbour on Monday, reaching as far as Maungatapu that night and coating a black shag in oil. The shag died two days later.
Fuel giant Mobil admitted the oil was theirs which had come from a leaking pipe while a ship was being refueled at the Port of Tauranga.