Diving pioneer and environmentalist Wade Doak is backing calls for a high-tech survey of the wreck of the Niagara, off Northland's east coast.
The big passenger liner was sunk by a German mine in June 1940, north of the Mokohinau Islands, and lies some 120m deep.
Mr Doak has authored several books on diving and is known for his advocacy for the Poor Knights Islands marine reserve.
He said he has visited the Niagara several times and doubted contingency plans could deal with spilt oil if the hull suddenly collapsed.
"No-one actually knows just how much oil is still in the wreck or how fragile the hull is after 76 years on the seabed," Mr Doak said.
"I don't think we have the ships or equipment to deal with that," he said.
Salvers who have inspected the ship off Northland's east coast have said up to 1600 tonnes of oil could still be in the bunkers and the hull is deteriorating.
They warned that it could eventually implode, leaving an oil slick four times bigger than the Rena's that could devastate beaches and birdlife from the Poor Knights Islands to the Hauraki Gulf.
Maritime New Zealand (MNZ) and its Minister Simon Bridges have deflected the concerns of the conservation boards in Auckland and Northland who want the wreck cleaned up.
In a letter to the Auckland Conservation Board Mr Bridges said monitoring of the wreck had found minor amounts of oil had leaked and naturally dispersed with no observed environmental impact.
"Due to the depth of the wreck and the type of oil on board it is likely the oil is in a near-solid form for much of the time and as it is likely distributed over a number of spaces and compartments.
"Contingency plans are in place that collectively cover the risks and response plans for an oil spill from any source in the Hauraki Gulf including the Niagara wreck," Mr Bridges said.
Mr Doak said Maritime New Zealand had never commissioned an inspection of the wreck and could not be sure it was low-risk.
He said no-one, including MNZ, knew the quantity of oil in the wreck, or the state of the hull.
"There needs to be a proper, salvage-style evaluation to find out if there's oil there, and if there is, it needs to removed safely," Mr Doak said.
"Basically I think just listen to what the salvers are suggesting and do it."
Mr Doak said other wartime wrecks around the Pacific had been cleaned up but the one in Auckland and Northland's front yard had been ignored.
He said oil bubbled up constantly from the Niagara, and he was mystified by Maritime New Zealand's belief the fuel was in a near-solid state most of the time.