Mr Fowler said crop diversity was imperilled not just by a cataclysmic event, such as a nuclear war, "but also by natural disasters, accidents, mismanagement, and short-sighted budget cuts". The vault will be built deep in permafrost in the side of a sandstone mountain on the Norwegian island of Spitsbergen, 1,000km from the North Pole.

Norwegian Prime Minister Jens Stoltenberg will take part in a ceremony of laying the first brick, together with leaders from other northern European countries. A metre of reinforced concrete will fortify the chamber walls. Arctic permafrost will act as a natural coolant to protect the samples which will be stored in watertight foil packages should a power failure disable refrigeration systems. The thick walls, airlocks and doors mean that even if global warming accelerates badly, it would take many decades for hotter air to reach the seeds.

So the seeds can survive for hundreds, and in some cases thousands, of years. Despite the top-level security arrangements the seed bank will not be under constant guard, except for the numerous polar bears which roam the area.

"It will ultimately house replicates of every known crop variety, as well as have ample capacity to accommodate new variation as it arises naturally," the statement says. "Enveloped by permafrost and rock, the samples will remain frozen even if electricity fails. Samples held in 'black boxes' will only be released in the event that all other seed sources have been destroyed or exhausted." The UN Food and Agriculture Organisation is part-funding the project, also known as an agricultural "Noah's Ark".

When launching the project, Norway's Agriculture Ministry had pointed to the fact that many of the 1,400 gene banks scattered around the world were in developing countries and could come under threats such as famine, natural and man-made disasters. While the seed banks' status varies greatly, many, the trust said, are in dire straits, threatening the survival of some of the world's unique crop varieties.

AFP