A "doomsday" vault storing crop seeds in an Arctic deep freeze is surpassing 500,000 samples to become the most diverse collection of food seeds in history, managers said yesterday.

Set up on the Norwegian archipelago of Svalbard two years ago, the vault aims to store seeds of all food crops deep beneath permafrost to withstand threats ranging from a cataclysmic nuclear war to a mundane power cut.

"New seeds... are taking us over the milestone of half a million samples," said Cary Fowler, head of the Global Crop Diversity Trust which runs the vault with the Norwegian government and the Nordic Genetic Resource Centre in Sweden.

A statement said thousands of new arrivals this week made the vault "the most diverse assemblage of crop diversity ever amassed anywhere in the world." It overtakes the diversity in a US national gene bank in Fort Collins, Colorado.

Among arrivals were a bean from South America that may have strong resistance to diseases, a strawberry from Russia's remote Kuril Islands in the Pacific and samples of soybeans from the US.

Only about 150 crops are grown widely around the world but all come in a wide range of varieties - potatoes, for instance, come in an array of sizes and colours.

The $10 million facility opened in 2008 with 268,000 varieties of seeds from more than 100 countries.

The three vault rooms will be able to house 4.5 million samples, or two billion seeds since samples usually comprise many seeds, such as of rice, maize, wheat, cowpea or barley.

Blasted out of icy rock 1,000kilometres from the North Pole, the air-locked vaults would stay frozen for 200 years even in the worst-case scenario of global warming and if mechanical refrigeration were to fail, designers say.

Dr Fowler said the vault was becoming more important after a UN climate summit in Copenhagen in December failed to agree a binding treaty to cut greenhouse gas emissions.

He said the collection could help in work to develop new crops that may contain traits able to withstand rising temperatures, floods or droughts that may be caused by rising temperatures in the 21st century.