Workers in protective gear cleaned parts of the shoreline in Maungatapu, piling oil-coated vegetation and debris into plastic bags along the shore.
Tauranga-based MP Clayton Mitchell has blasted Mobil's "spin doctoring" over how much oil has leaked into the harbour.
The New Zealand First MP said finding out how much fuel had ended up in Tauranga Harbour should be simple.
"They will be able to work that out. They aren't telling us because they are trying to spin it to make it sound like it's not a major deal when it is a major deal," he said.
"It's just filibustering. They are spin-doctoring it."
But a Mobil spokesperson said the amount of oil would be hard to determine because the leak in the pipe was located before the fuel meter.
Mobil has said it checked the pipelines every three months, but Mr Mitchell said quarterly checks were unacceptable.
Systems needed improving to ensure such a leak never happened again, he said.
"The impact this will have on the tourism sector - we've all felt the effects of the back end of the Rena. Now we're again being hit with images of oil in our beautiful harbour."
Mobil said a meter measured how much oil went through the pipe into ships being refuelled - but the leak occurred before the meter.
This made estimating how much oil had spilled into the harbour much harder to calculate, the spokesperson said.
Image 1 of 8: A large slick of oil can be seen at Tauranga Marina. Photo/Amanda Witherell
"In some senses, the volume itself is irrelevant, it's whether the response is appropriate. In this case, we can be absolutely confident the Bay of Plenty Regional Council has manned an excellent response."
Bay of Plenty Regional Council's on-scene commander Peter Buell said officials were continuing clean-up operations without knowing exactly how much oil had been released into the enviroment.
"While it would be useful to know the amount of oil spilled, this information isn't critical to our response. We completed rapid shoreline and on-water surveys to give us a clear picture of the scale of the oil spread and enabled us to put our response plan, trained staff and specialised equipment in place effectively.
"By the end of Wednesday we had collected approximately seven tonnes of oil-covered sand, vegetation and other debris."
"Approximately 70 staff, volunteers, iwi and contractors have continued work at Maungatapu, Tauranga Bridge Marina and the port to collect oil using sorbent booms, pads, skimmers and shovels."
Mr Buell said the confirmed effects on wildlife had been limited to date.
"There have been just two shags and one penguin captured and needing treatment for oiling. The penguin has recovered and will be released this evening."
Mr Buell said the extent of the spill and damage was being studied.
"Scientists from Bay of Plenty Regional Council and University of Waikato accompanied by iwi have been investigating this and taking samples with a particular focus on shellfish and sea grass. It will be a few weeks before analysis of the first sampling round is completed."
He added the long-term impacts would need to be considered but, for now, the focus was on cleaning up as much as possible.
"We continue to be focused on cleaning up as much oil as possible, using every appropriate method. Our science team are starting to investigate what the long-term impacts - if any - might be."
The oil leaked from two holes about 4mm in diameter on a 3m-long pipeline that branches off a main pipeline along Mount Maunganui Wharf. The network carried heavy fuel oil for ships.
It would be a week or two before engineers could estimate how much fuel was spilled.
Image 1 of 15: Regional council workers Nathan Capper left and Reece Irving tying up bags. Photo/George Novak
The pipes were checked last month as part of a quarterly maintenance programme, the spokesperson said.
"The March test didn't identify any issues so the investigation is trying to understand why it happened. The pressure test conducted would have picked up that kind of problem."
Mobil believed Tauranga was one of only two ports in the country to have such a pipeline.
"There are not that many fuel lines in New Zealand that carry bunker fuel. We have shut down the whole pipeline system to the wharf and are looking at all sections of pipeline that run off the main line and testing those.
"We won't be putting them back into service until we are absolutely sure there are no issues."
The spokesperson said the pipeline system would continue to be used.
Tauranga MP Simon Bridges, when asked if it was safe to use a system that could develop a leak in one month, said in a written statement: "Maritime NZ is currently providing Bay of Plenty Regional Council with technical assistance to assess the processes used by Mobil in the case. This will include the inspection regime for the pipe and how this was administered.
"The council has stopped this line being used until the investigation is complete."
Mr Bridges said it was not feasible to use portable bunkering for a large ship.
"For instance, in this case, the ship was taking on 500 tonnes of heavy fuel oil, and a road tanker carries only around 20 tonnes."
Green Party conservation spokesperson Eugenie Sage said the spill highlighted how damaging oil and gas exploration could be on the environment.
"Mobil can't tell us how much oil has been spilt from their corroded pipeline into Tauranga Harbour. It begs the question as to how companies would cope if there was a larger spill from deep-sea oil exploration - a particularly risky endeavour."
Ms Sage said it had been five years since the Deep Water Horizon oil spill in the Gulf of Mexico, but the impact on wildlife was still being felt.
"When the Rena ran aground off the Bay of Plenty coast, the impact was overwhelming. Some 2000 dead birds were found, and up to 20,000 birds are thought to have been killed. Taxpayers paid nearly $48 million in the aftermath of the disaster," she said.
