Environment Minister Nick Smith says the process of pumping oil off Rena is too slow and he believes there will be more dangers ahead.
But salvage operators say that trying to increase the pumping speed is difficult.
Mr Smith, who was aboard the HMNZS Pukaki yesterday, said he was still waiting for positive news of increased pumping speeds.
"I'm still not satisfied with the pumping rates. I'd be wanting to see pumping rates of 10 tonnes an hour. We're hoping, with the booster rate, it'll get better," he said.
Mr Smith said he was most concerned with the tanks on the starboard side of the Rena which he believed could release a fresh wave of environmental damage. And even after the oil has all been removed, he said the ship will remain a hazard.
"I'm quite worried with the complexities of getting the oil out of the starboard side.
"There's 355 tonnes in that starboard tank that has the capability to unleash a death wish on another thousand birds.
"The Government will breathe a huge sigh of relief when that heavy oil is removed off that ship," he said.
Having spoken with Maritime and the salvors, Mr Smith said the Rena is likely to remain an eyesore for Mount Maunganui and Papamoa residents for a long time to come.
He said the removal of the containers is likely to take a long time, although the container operation cannot even begin until the oil is extracted.
"In my view it [the container removal] is shaping up as the biggest challenge ahead. I think we need to prepare the Bay of Plenty for the long haul.
"We'll be talking many months of work to remove the containers," he said.
And even after that, he said, the Rena may still blight the waters off the coast.
"The moment that Rena hit the reef it was a disaster in slow motion," he said.
"I suspect the Bay of Plenty is going to get a new reef. Albeit an unwelcome one."
Maritime New Zealand salvage unit chief Bruce Anderson said the crews pumping oil from MV Rena have called in help to try speed up the pumping rate.
"They are going to look at how they can speed things up.
"The pump manufacturers are sending one of their specialists out ... so they can get every ounce of flow," he said yesterday.
Mr Anderson said the pumps had been working non-stop since midday on Thursday.
At least one of the booster pumps that had been added to the 160m hose to increase flow had faulted but, because the oil hose had safety loops which can redirect the oil back into the tanks, the primary pumping had not been halted.
The boosters were replaced and the flow to the Awanuia tanker has been consistent. Maritime New Zealand could not confirm pumping speeds but thought the pipes were flowing faster.
Svitzer salvage master Drew Shannon said his crews were constantly trying to improve the oil extraction speed.
"We're looking for ways to continue improving the pump rate.
"We're working on the highest priority, which is the port side and the engine room. "The pumping rate could be better. It could also be worse," he said.
The plan is to empty the port side oil tanks before tackling the more difficult, submerged starboard side.
The starboard side is largely underwater but, even so, salvors still believed the oil from its tanks could be removed once divers had assessed the internal risks, Mr Shannon said.
Salvage crews have been working around the clock on the ship with teams of three being airlifted on and off.