In the belly of a mountain halfway between mainland Norway and the North Pole lies a seed repository that could one day save the world.

The Svalbard Global Seed Vault, also known as the doomsday vault, is the largest of its kind anywhere and it holds seeds of value for food and agriculture, including rice strains developed in Singapore.

Built to outlive any disaster, natural or man-made, the permafrost stronghold sits on a remote Arctic island in the Norwegian archipelago where polar bears roam. It is a safe haven for the earth's most precious food resources, ranging from rice and wheat to maize and barley.

The vault holds nearly a million seed samples from the world's gene banks - and acts as an agricultural backup against events ranging from nuclear war to natural disasters. When it is full, it will have some 4.5 million seed samples, each consisting of about 500 seeds, or a total of about 2.25 billion seeds.

With climate change causing increasingly erratic weather and threatening crops the world over, the vault is now more critical than ever.

Svalbard Global Seed Vault coordinator Asmund Asdal said: "Plant genetic resources are crucial for future food production, in particular to adapting agriculture to climate change.

"The genetic resources conserved as seeds in gene banks and in addition copied in the Svalbard Global Seed Vault are an insurance for feeding future generations with enough and healthy food."

Plant breeders and researchers depend on seed banks around the world to obtain varieties with useful traits they need. If those seed banks later lose their own resources, the collections could be restored by getting the copies back from Svalbard.

In fact, the vault has already provided valuable replacement seeds for those that were destroyed in Syria during the war, which were taken for re-cultivation in Lebanon and Morocco. Last year, around 14,000 packets of grains and legume seeds were returned to the vault.

In 2016, Singapore made its first deposit.

The seeds of seven unique rice varieties, with traits to overcome challenges such as drought or fungus, for instance, were contributed by local research outfit Temasek Life Sciences Laboratory (TLL) and represent its efforts towards boosting long-term food security.

A TLL spokesman said it will consider depositing more seeds into the vault, as it continues research into new and improved rice varieties to enhance yields and farm productivity, as well as expanding its agriculture portfolio to include other crops.

Carved deep within the rock recesses of the "Plataberget" (plateau mountain), the 10-year-old facility, which was built at a cost of about US$9 million, is owned and administered by the Norwegian government.

The Global Crop Diversity Trust (Crop Trust) supports ongoing operations and the Nordic Genetic Resource Centre (NordGen) operates the facility and maintains a public online database of samples.

Svalbard was seen as an ideal location for the vault because of its remote location and cold, dry climate.

But even the vault's defences felt the bite of climate change recently.

An unexpected thaw of permafrost in late 2016 meant water flowed into the entrance of the vault's tunnel. Although the seeds were safe, the vault is being upgraded as part of a long-term plan to enhance the performance and extend the viability of the facility.

Crop Trust executive director Marie Haga said: "Climate change and population growth pose one of the greatest challenges ever to food production."

Agriculture worldwide has to adapt to new pests and diseases, higher temperatures, less water and soil degradation, while providing more nutritious food to more people, she pointed out.

"The farmers of the world will need crop diversity to do so. Safeguarding such a huge range of seeds in the Svalbard Global Seed Vault means scientists will have the best chance of developing nutritious and climate-resilient crops that can ensure future generations don't just survive, but also thrive."