"This seed bank is of global importance," Norwegian Prime Minister Jens Stoltenberg said at the ceremony to mark the start of construction on a windswept mountain on the Svalbard archipelago overlooking fjords and glaciers.

"It's our final safety net. If seeds stored in a commercial gene bank are destroyed, and this has apparently happened about 40 times to date, the contents of this gene bank will make it possible to replace the seeds which have been lost," he said.

Lying about 1,000 km (600 miles) from the North Pole, Svalbard is a desolate, treeless archipelago where farming is impossible. Norway controls the islands and has agreed to pay the US$3 million construction bill.

The Rome-based Global Crop Diversity Trust, headed by American Cary Fowler, will manage the site when it opens next year.

The trust is a joint initiative of the International Plant Genetic Resources Institute and the UN Food and Agriculture Organisation to support crop diversity and help secure food for the world's population.

"This is a very remote location, you need that for security purposes," Fowler said. "Also Svalbard is operated by the Norwegian authorities, there is good infrastructure here, the Norwegians are volunteering to build the facility and it offers this tremendous advantage of permafrost."

The vault's temperature would be maintained at minus 18 degrees Celsius (-0.4 fahrenheit), the optimum for seed preservation, Fowler said, and if the power failed the natural permafrost would keep the temperature below freezing.

If a crop type is lost through natural disaster or war and a seed bank is destroyed, a government could request replacement seeds from the vault, Fowler said.

There were hundreds of different unknown gene types among crops that could be adapted in the future to cope with environmental changes and population pressures, he said.

Fowler told Reuters that wars in Iraq and Afghanistan and the 1994 genocide in Rwanda wiped out dozens of unique crops and destroyed those countries' national seed banks, which meant the genes had been lost for ever.

"You can use the word extinction in this case," he said.