The prospect of a devastating oil spill from a sunken World War II wreck along some of our most beautiful coastline has been raised in an artist's exhibition which calls on the government to take action.

And new documents show Minister of Conservation Eugenie Sage is raising conservation questions on an issue which saw little advice provided to her predecessors.

The RMS Niagara - known as the "Titanic of the South Pacific" - lies in 120 metres of water off the Hen and Chicken Islands in the northernmost part of the Hauraki Gulf.

It sank after striking a mine in 1940 with $500 million worth of gold on board and an unknown amount of oil.

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But it is believed at least 1000 tonnes remain in the hulk - more than three times the 300 tonnes MV Rena spilled across beaches and reefs around Tauranga in 2011.

The exhibition is called "Gold and Oil: The Legacy and Menace of the Niagara" and opened on Thursday at the Mangawhai Artists Gallery. It runs until February 21.

Artist Nicola Everett said the exhibition came out of a desire to express an opinion on the wreck and the danger it posed to the environment.

"I wanted to make more people aware of this issue - this time bomb sitting out there."

Nicola Everett only became aware of the potential oil spill five years ago.
Nicola Everett only became aware of the potential oil spill five years ago.

She said the story of the Niagara and the threat it posed was not well-known and was something she had only become aware of five years ago.

"I have a sense there is a terrible potential there for devastation we could do something about."

Everett said she wanted the wreck to be regularly monitored rather than relying on passing vessels to report any oil that had escaped.

But she said ultimately, it had to be removed.

"It's not 1940 - the oil won't be carried away into this wondrous ocean that seems to swallow all the rubbish we throw at it.

"Better to do something about it than wait and say we will clean it up afterwards."

The exhibition actively seeks to engage politicians on the issue with forms of support for people to fill in which would then be sent to Parliament.

For all that, Everett said none of the many MPs invited to attend the opening turned up.

The Auckland Conservation Board and Northland Conservation Board have urged the government to take action on the wreck.

Auckland councillor Mike Lee has been a strong advocate for removing the oil, telling the Herald there was an increasing possibility of the ship's bulkheads collapsing.

"The tanks holding this bunker oil are likely corrupt and a lot of oil will come up at once."

He said there were estimates it contained as much as 1600 tonnes of oil and there was a need to get precise information on the condition of the wreck.

An Investigation by the NZ Herald of documents spanning the 78 years since the Niagara sank recorded the extraordinary and secretive efforts to recover the gold.

But similar efforts have not been undertaken to get the oil off the ship and some observers have reported slicks emerging from the wreck, stretching for kilometres.

Maritime NZ's assessment of the Niagara found there was no immediate risk of a massive oil spill and there were sufficient containment and clean-up resources if it should disgorge its load.

The type of oil and the depth it is at led experts to conclude it was unlikely to come to the surface, although a new plan was developed in 2016 to deal with a potential spill.

New information released under the Official Information Act shows the Department of Conservation conceding that it has had "limited involvement in the management of the Niagara wreck".

It had refused to engage in public comment on the issue, deferring to Maritime NZ as the agency responsible for wrecks.

In a briefing to Sage, Conservation officials said they expected the government's stance to be criticised in the Herald investigation.

As a result of the briefing to Sage, the department's position was shifting.

Conservation Auckland operations director Andrew Baucke said the briefing had led to Sage directly dealing with associate transport minister Julie-Anne Genter on the issue.

"While Department of Conservation staff have been monitoring the situation to assess potential risks to marine and bird life, to date it has not been a subject for a great deal of Ministerial advice."