A promise by global krill harvesting companies they will stop fishing for the small crustacean in large areas of the Antarctic Ocean is a positive step in a long process, Greenpeace says.

New Zealand companies are among the global move, which is part of a campaign to create the world's biggest marine reserve in Antarctic waters.

The move was announced this month at Greenpeace's Antarctic 360° event in the UK.

Antarctic scientists are now drawing up the technical plans for marine protected areas in the Antarctic Ocean, one of which is expected to cover about 1.8 million square kilometres in the Weddell Sea.

Greenpeace says fishing for Antarctic krill is permitted in the Antarctic Ocean under the management of the Commission for the Conservation of Antarctic Marine Living Resources.

Krill is described as a keystone species in the Antarctic food web, eaten by penguins, seals, whales and other marine life.

Greenpeace New Zealand spokesman Phil Vine says the promise by 85 per cent of krill companies to fish sustainably in the area was an "amazing and brave step", but there was still a long way to go.

"At the moment their promises are just voluntary ones, so what we want to do is enshrine this promise in an actual international law which creates these sanctuaries so they cannot be touched."

Greenpeace is also calling on krill-buying companies to stop sourcing from vessels that continued to fish in the areas.

Phil says a Nelson-based nutraceutical company which used krill was among those supporting the move, however RNZ has so far been unable to reach senior management for comment.

'Without krill we have nothing'

The ultimate aim is to create a connecting chain of marine reserves, beginning with that planned in the Weddell Sea - which would be the biggest reserve in the world.

Phil says krill is the basis of the food chain for all wildlife in Antarctica: "It's absolutely crucial it's kept intact. Without krill we have nothing - everything will go."

Greenpeace is encouraging the remaining 15 percent of industries which fished for krill in the area to get on board with the plan.

He declined to say which ones they were.

"We're hoping they will step up and follow the example of the rest of the fleets."

New Zealand is a member of the Commission for the Conservation of Antarctic Marine Living Resources, which will vote on the proposed reserve in the Weddell Sea.

The final decision will be taken by the commission in October 2018, when it meets in Tasmania.