Two of the world's most vulnerable low-lying island nations, Kiribati and Tuvalu, have said failure at upcoming climate talks in Paris is not an option as rising sea levels threaten their very existence.

The Pacific island nations say they have been forced to consider such nuclear options as buying land abroad to grow food and preparing their people to migrate as the seas slowly claim their homelands.

But as representatives of Pacific island nations met in Jaipur in the western Indian desert state of Rajasthan this week, the message was clear -- world leaders meeting in Paris in December must deliver on expectations of a historic deal to combat global warming.

"Failure is not a fallback position, it is not an option, we cannot have it as an option. We must get success," Tuvalu Prime Minister Enele Sopoaga told AFP in an interview.

"We may be able to run away, we may be able to purchase land in other places, maybe Australia, New Zealand.

"But that won't stop climate change, it will not stop the cause of climate change. It will not assure the people of Tuvalu that they will be safe there."

Sopoaga said climate change was now "enemy number one for Tuvalu", nine coral atolls that are home to about 11,000 residents.

Scientists predict Tuvalu and Kiribati, which are little more than a metre (three feet) above sea level, could disappear in the coming decades.

Both nations already suffer from a range of problems linked to climate change, including more intense storms like the one that devastated Vanuatu earlier this year and salination of ground water, which makes it impossible to grow crops.

- 'It's too late' -

The situation is so dire that Kiribati is considering relocating the entire population, or building man-made islands to rehouse them.

"For us we think that things have progressed, have advanced too much, it's too late for us," Kiribati's special envoy Teekoa Luta told AFP in Jaipur, where representatives of 14 Pacific nations held talks on Friday.

"Paris we hope will buy us some time, but we are not positive that anything that is achieved in Paris, the outcomes would be in time for us."

The UN conference in Paris will seek to crown a six-year effort by 195 nations with a post-2020 pact on curbing greenhouse gases.

But Luta said her tiny nation of 100,000 people was already struggling to cope with the fall-out from climate change.

"Our resources are constrained, our institutional capacity to cope with our health problems are constrained," she said.

"We spend most of our budget fixing the (natural) damages month after month and then we don't have money to spend on health, education and (other) social services."

Kiribati recently called for a global moratorium on building new coal mines and expanding existing ones -- a move Luta said she hoped that major economies including India would eventually support.

New Delhi has courted the Pacific island nations as it seeks to win back influence in an area of the world increasingly dominated by regional rival China.

In a speech to delegates on Friday, Prime Minister Narendra Modi offered to illuminate thousands of Pacific island homes with solar power and highlighted India's own plans to ramp up its renewable energy output to 175,000 megawatts by 2022.

But India, the world's third-largest contributor of greenhouse gases, has so far resisted committing itself to any major emissions cuts and Modi has bet big on coal, a key source of emissions.

Nonetheless, Luta welcomed India's "positive" comments and said the country of 1.2 billion people had shown it was "committed to take up the action, to walk the talk as they say".

- 'Crazy options' -

Luta said Kiribati is already beginning to train its people with skills so that "in the event that they have to migrate, that they migrate with dignity and do not become a liability to the receiving country".

The former British colony has also bought 2,000 hectares (5,000 acres) of land in Fiji to farm if salt-water pollution means it can no longer produce crops.

"We're talking about relocation and there are ideas that maybe we should try making floating islands... People will sometimes think that we're crazy but I think we become desperate at times, and therefore have all these crazy options," Luta said.

Both nations said they were working to counter rising water levels by building sea walls and planting mangroves, but that only global cooperation in Paris could save them.

"We need to have this Paris agreement because otherwise there won't be any survival processes to save the people on these islands," Sopoaga said.

"We do it now together or we all fall."