Defences at Norway’s “Doomsday vault” where thousands of varieties of crop seeds are stored in case of natural disaster are to be reinforced.

The move follows water gushing into the tunnel entrance after the permafrost melted last year.

Although no seeds were damaged there is concern that the the vault, which is buried deep inside a mountain near the Norwegian island of Spitsbergen, could be vulnerable.

The reinforced defences will see new waterproof walls being built inside the tunnel and drainage ditches outside the entrance.