Talks to create the world’s two largest marine reserves in the Antarctic could be undermined by a last-ditch push for a “sunset clause” that would allow protections from fishing and oil drilling to be stripped away in the future, conservationists have warned.

Negotiations at a meeting of the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR) began in Hobart on Wednesday, with delegates from 25 member nations thrashing out details of the exact scope of the two reserves.

A proposal backed by the US and New Zealand would create a 1.3 million sq km “no take” zone in the vast Ross Sea, one of the last pristine bodies of water in the world.

A separate plan, put forward by Australia, France and the European Union, proposes to establish a 1.6 million sq km sanctuary in East Antarctica’s marine environment. Combined, the two reserves will be equivalent to the size of India and will double the 1% of the world’s oceans that are currently protected.

The reserves have to be agreed by consensus. The Hobart meeting is the third time the plans have been discussed since October last year. The Ross Sea protected zone has been shrunk by 40% in order to reach agreement.

A coalition of 30 conservation groups say the reserves are needed to provide long-term protection to the seas around Antarctica from oil drilling and fishing. The waters are home to more than 10,000 unique species, including the vast bulk of the world’s penguins, whales, seabirds and the Antarctic toothfish.

However, there are concerns that a “sunset clause”, put forward by New Zealand, could allow future exploitation of Antarctic waters.

“We are worried about the permanence of the marine protected areas as there is talk of 15 years or 50 years as a sunset clause,” Andrea Kavanagh, director of the Pew Charitable Trusts’ southern ocean sanctuary campaign, told Guardian Australia.

“These areas need to be permanent, any less than that is not good enough. Some countries are more comfortable with a sunset clause but that’s not how the ecosystem works. If you think of the life of some of these species, such as deep sea corals and toothfish, 15 years is ridiculous.

“I’m optimistic that we are close to a final agreement but I’m a little nervous about the permanence question. Countries are agreeing on boundaries and management first, which is understandable, but if time is squeezed, the sunset clause could become a real issue.”

Negotiations have hit several stumbling blocks, with Russia and Ukraine previously questioning the legal basis of the plan. Meanwhile, Norway is understood to have reservations about the zones due to the limits they would put on the country’s fishing fleet, which currently scoops up vast amounts of krill off the coast of the Antarctic in order to feed its salmon farms back home.

Jim Barnes, director of the Antarctic and Southern Ocean Coalition, said: "Agreeing on large marine protected areas in the Ross Sea and East Antarctica is a key test of whether countries honour their international commitments.

“The science supporting the two proposals is compelling, and it is only short-term economic gain that is blocking consensus."

Talks will continue until 1 November.