Amid growing security concerns over Russia's nuclear threat and North Korea's missile ambitions, a nonprofit organization in Japan has built a model nuclear shelter near Tokyo 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 Tsukuba, Ibaraki Prefecture. It has already hosted about 40 tours by 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 last year, it said, with its membership rising from just two companies to around 30 in over a year.

Photo taken on June 27, 2023, shows the exterior of a model nuclear bomb shelter situated outside the Japan Nuclear Shelter Association in Tsukuba, Ibaraki Prefecture. (Kyodo)

"We were thinking about building this even before the (Russian) invasion of Ukraine, but decided we really had to from spring last year," said director Takahiro Kawashima.

The facility is built to specifications from Switzerland, where 1960s legislation at the height of the Cold War required shelters be made available to all citizens.

The structure can withstand a blast like the 1945 atomic bombings of Hiroshima and Nagasaki, provided it is just under a kilometer or more from the explosion's center, according to the association.

It says the underground shelter can house a family of four adults, three children and one pet for a maximum of two weeks. While the entire space is about 48 square meters, its living area is around 25.6 square meters.

Amenities include a portable toilet, an air filtration system and a 200-millimeter-thick blast-proof door. Its foreign specifications present limitations, though, with the association saying Japanese building rules on hot water in enclosed spaces mean any shower in the unit can only run cold.

Photo taken on June 27, 2023, shows an underground living space capable of accommodating a family of four adults, three children and a pet inside a model nuclear bomb shelter in Tsukuba, Ibaraki Prefecture. (Kyodo)

The Cabinet Office considers below-ground facilities more effective than surface ones in reducing the effects of air blasts. But a Kyodo News survey on local governments in January and February found that of 59,132 facilities designated as emergency shelters, just 2,390 of them -- or about 4 percent -- are underground.

Discussion among political figures about the construction of bunkers has accelerated in Japan as Russia's aggression in Ukraine created fears of nuclear war. Those worries were only exacerbated by the potential for conflict between China and Taiwan in the coming years.

The threat from North Korea has also ramped up after it launched missiles, including intercontinental ballistic missiles, on a record 37 occasions in 2022, in some cases prompting alerts recommending people seek shelter in some parts of Japan.

The situation has led to the establishment of a group of ruling Liberal Democratic Party lawmakers calling for the government to provide financial support for establishing shelters in municipalities that host armed forces' bases. They presented their proposals to Prime Minister Fumio Kishida in June.

But it remains unclear how much a system like the one the association is showcasing would cost if it became a national standard.

Construction of the model shelter came in at a total of around 40 million yen ($277,000) to build and outfit but the organization maintains that a more standard price would be around 20 to 30 million yen per unit, not inclusive of the land on which it is constructed.

Due to the demand for tours, Kawashima said there has not yet been an opportunity for anyone to try staying in it. "We are thinking about asking someone to try living down there for the full 14 days -- perhaps a YouTuber or someone like that," he added with a laugh.