Foreign Affairs Minister Murray McCully says New Zealand is still hoping for agreement among 25 countries to restrict fishing in the Ross Sea, one of the last intact marine ecosystems in the world.
However, Mr McCully says the range of views on the issue means there is a real risk there will be no agreement.
New Zealand is being criticised by environmentalists for not signing up to a US proposal that would strengthen protection for Antarctic toothfish.
The New Zealand Government has its own proposal for a Marine Protected Area, which would ban the fishing of toothfish within the zone and allow it to continue outside it.
Mr McCully says there will be further discussions next month and he had assured US Secretary of State Hillary Clinton that New Zealand would work closely with the United States.
"It's going to be a very complex and difficult process but I think New Zealand and the US will be able to co-operate very closely during the discussions.
"But as I say, there are 25 players in the room, we have to get the agreement of all of them, and that's still going to be quite a challenge."
Mr McCully says there are a range of interests involved including conservation, science and the fishing industry.