New Zealand on Wednesday dismissed a call from top marine scientists to better protect a rare dolphin, saying existing safeguards for the creature dubbed "the hobbit of the sea" were sufficient.

The International Whaling Commission's (IWC) scientific committee, representing more than 200 marine experts, has warned that the Maui's dolphin will become extinct unless fishing is banned in its habitat.

Researchers believe only around 50 Maui's dolphins are left in their sole range -- shallow waters off the North Island's west coast -- and they estimate three-to-four are accidentally killed as fishing by-catch every year.

Conservation Minister Nick Smith disputed the figure, saying that a ban on set-netting covering an area of 6,200 square kilometres (2,400 square miles) had been effective in minimising deaths.

While the IWC wants a total fishing ban in a larger area extending 20 nautical miles from the coast, Smith said there was no evidence the dolphins were found outside the area that was already protected.

"Effectively, they are asking us to shut down the entire fishing industry all the way up the west coast of the North Island, way beyond areas where we have any evidence that the Maui's dolphin are," he told Radio New Zealand.

"I am not going to get in the business of banning fishing (in areas) where there is no evidence Maui's dolphin exists."

The grey and white Maui's, named after a Polynesian demi-god, is the world's smallest and rarest dolphin, with a maximum length of 1.7 metres (5.5 foot).

Smith denied it was hypocritical of New Zealand to criticise Japan's so-called "scientific" whaling programme when it was refusing to abide by the IWC's recommendations.

New Zealand and Australia won a United Nations court order banning the Japanese programme earlier this year.

"I think it's a very big difference between the International Court of Justice that has made the decision in respect of the Japanese whaling and a technical committee of the International Whaling Commission," Smith said.

Conservation group NABU International said the IWC was only one of a chorus of scientific bodies, including the Society for Marine Mammalogy and the International Union for Conservation of Nature, which said the evidence showed the dolphin needed more protection.

"Nick Smith's fantastical stance that everyone apart from him and New Zealand's fishing industry is wrong about this is fooling no one," NABU endangered species specialist Barbara Maas told AFP, saying New Zealand's "clean, green" image was at risk.

"It's high time to stop playing politics, embrace the facts and get serious about saving the last 50 Maui's dolphins. Otherwise, this government will forever be culpable of wilful extinction."