Amid growing security concerns over Russia's nuclear threat and North Korea's missile development, a nonprofit organization in Japan has built a model nuclear shelter in Tsukuba, Ibaraki Prefecture, to raise awareness and encourage people to consider digging a doomsday bunker of their own.

While not yet open to the public, the underground concrete structure opened on May 10 in a parking lot opposite the Japan Nuclear Shelter Association's office in the city. It has already hosted about 40 tours for construction professionals, national and local politicians, government agencies and the media.

The association says it aims to see shelters built in Japan to established standards. Interest in its activities has exploded recently, it said, with its membership rising from just two companies to around 30 in over a year.