Marine scientists have called on New Zealand immediately to ban fishing in waters inhabited by the world's rarest dolphin, saying that losing just one more of the creatures will threaten the species' existence.

The Maui's dolphin is one of the world's smallest, with a maximum length of 1.7 metres (5.5 feet), prompting conservationists to call it "the hobbit of the sea".

Found only in shallow waters off the North Island's west coast, it is listed as critically endangered with just 55 adults remaining and there are fears it will disappear by 2030 unless urgent action is taken.

The International Whaling Commission's (IWC) scientific committee said it was extremely concerned about the dolphin's plight, adding: "The human-caused death of even one dolphin in such a small population would increase the extinction risk for this sub-species."

While the New Zealand government has previously said it would consider both the risks facing the dolphins and the impact on the local fishing industry before implementing a management plan, the IWC said there was no room for delay.

"Rather than seeking further scientific evidence, the priority should be given to immediate management actions that will lead to the elimination of bycatch of Maui's dolphins," it said.

"This includes full closures of any fisheries within the range of Maui's dolphins that are known to pose a risk."

The organisation, which made a similar plea to ban fishing last year, noted that proposals for seabed mining, including seismic surveying, also represented a potential threat.

The call for action was contained in a report published over the weekend which revealed for the first time the recommendations of the IWC's annual meeting in South Korea last month.

Barbara Maas, an endangered species specialist at Germany-based conservation group NABU who attended the meeting, said there could be no more stalling if New Zealand wanted to save the dolphin.

She told AFP on Monday that the country was willing to spend tens of millions of dollars promoting itself as the home of "Middle Earth" and "clean and green" but needed to back up the marketing with action or risk tarnishing its image.

"There's no time to lose here, we're already down to 15 adult females, we're losing them," she said.

"We're looking at a species of dolphin going extinct in a country that advertises itself as 100 percent pure... it's all very well faffing around with a fictitious hobbit, but here you have the hobbit of the sea, the smallest dolphin in the world, that needs saving."

Three movies featuring J.R.R. Tolkien's fictional characters have been filmed in New Zealand, with one released so far. Tourism officials launched a major promotion on the back of the movies.

The local fishing industry disputes allegations it is to blame for the dolphin's demise, saying it has become a scapegoat while other explanations such as the parasitic disease toxoplasmosis are ignored.

Greenpeace oceans campaigner Karli Thomas said the Maui's dolphin risked joining the Yangtze River's Baiji, a freshwater dolphin that was declared extinct in 2006.

"If Maui's dolphin disappears because of this government's inaction, it will make New Zealand only the second country in the world, after China, to drive a dolphin species to extinction," she said.

Maas said the issue boiled down to money, with the fishing industry keen to continue and the government reluctant to pay compensation if it was forced to close.

"They're trying to kick this down the path until there's nothing left to save," she said.

Conservation Minister Nick Smith said the government hoped to release a management plan next month and wanted to "take all practical actions to ensure the survival of this very special species".

"(The IWC) wish to have the range of Maui's dolphin closed to fishing, the question is what is the range of the Maui's dolphin?" he said.