Dynamited out of a mountainside on Spitsbergen island around 1,000 km (600 miles) from the North Pole, the store has been called a doomsday vault or a Noah's Ark of the plant kingdom.
It is the brainchild of a soft-spoken academic from Tennessee who is passionate about securing food for the masses, and will back up seed stores around the world that are vulnerable to loss through war or disaster.
A 20-metre (66-foot) long concrete entrance, still under scaffolding, juts out of the snow-dusted mountain above the coal-mining town of Longyearbyen.
It is reached by a switchback road rising to 120 meters above sea level, offering spectacular views of the fjord below and snow-capped Arctic mountains beyond.
Visitors descend through the mouth of a gently sloping 40-metre steel tube into the frosty cavern which smells of new cement and is dotted with portable lamps as work progresses for February's opening.
"There aren't going to be any better storage conditions than what we will provide here," founder Cary Fowler told reporters during a recent visit to the site in the Svalbard archipelago off northern Norway. "This is a safety deposit box, like in a bank, where you put your valuables."
Although this is one of the world's most northerly settlements, an electric freezer will be used to keep the seeds in the three-chambered concrete-lined vault at minus 18 degrees Celsius (minus 0.4 Fahrenheit).
If the power fails, permafrost will still keep them frozen, but not as deeply.
The project is at the heart of an effort by Fowler's foundation, the Global Crop Diversity Trust, to safeguard strains of 21 essential crops, such as wheat, barley and rice.
Rice alone exists in about 120,000 different varieties.
Ultimately, it is part of the world battle against hunger, as crop insecurity mainly hurts poor nations.
"Crops important to the poorest of the poor have really been neglected," said Roy Steiner, an official at the Bill and Melinda Gates Foundation, which has provided financial support.
"Millet and crops like cow pea receive so little attention."
Fowler calls such varieties "orphan crops" because they have no one to take care of them.
The aim is to preserve genetic diversity, needed by plant breeders in the future to produce varieties able to adapt to challenges like climate change.
Crops consist of numerous species, some as different from each other as a "Dachshund from a Great Dane," Fowler said.
If such a store had existed 10 years ago, he said, the seeds would have been needed about once a year as seed collections have been wiped out -- for instance by a typhoon in the Philippines and war in Iraq and Afghanistan.
"I'm sorry to say we will be using it a lot," Fowler said.
Eventually, the vault will have capacity for around 4.5 million bar-coded seed samples and it hopes in its first year to collect half a million.
Not all seeds can be stored by freezing. Banana, the world's fourth or fifth most valuable crop, is one example.
"The longest viability under these conditions would be that of sorghum -- about 19,500 years," Fowler said. Other varieties will need to be replaced more frequently.
"We're trying to capture the diversity not just between different species but within different species -- that's the basis for evolution," said Fowler, an official of the U.N. Food and Agriculture Organization but his own boss at the Trust.
"Extinction happens when a species loses the ability to evolve."
Norway is contributing some 50 million crowns ($8.6 million) to build the cavern, a sum which Development Aid Minister Erik Solheim said was a pittance for what is gained.
"I consider it a development issue ... Poor African countries have fewer resources to protect their genetic heritage than rich countries," he said.
The Gates Foundation, the philanthropic giant created by the founder of Microsoft, has given a $30 million grant to Fowler's effort, including money for packaging seeds in their countries of origin and shipping them to the vault.
Some of Gates' money has gone to develop a new style of seed packet, a small silver-colored pouch made of a special foil and layers of other advanced materials to keep seeds dry and frozen -- the "Rolls Royce of seed packets," Fowler said.
The Gates Foundation is also helping develop two software systems, one to help manage seed banks and another to link them globally so that plant breeders can find what is available.
"Seeds are almost the software of the natural world that has taken millions of years to develop, and we don't know how we will need them in the future," the foundation's Steiner said.