Japanese firm proposes undersea city of 5,000 people

It sounds like an idea for a sequel to the hit science-fiction film Interstellar: an underwater city of 5,000 people that draws its energy from the seabed thousands of metres below.

But if a Japanese construction firm gets its way, Ocean Spiral could be a reality within just a couple of decades.

Shimizu Corp, which has a reputation for dreaming up grandiose schemes, says Ocean Spiral will "capitalise on the infinite possibilities of the deep sea" to accommodate human life, as rising sea levels threaten the survival of island communities.

According to an artist's rendering, the structure will be divided into three sections.

A floating sphere with a diameter of 500 metres, just beneath the surface of the sea, will house business and residential zones and hotels. The pod will be connected to a 15km-long spiral path that winds its way to the ocean floor 3-4km below the surface. There, scientists will explore ways to excavate energy resources from the seabed.

Officials at Shimizu said the project would take about five years to build, at an estimated cost of 3 trillion yen (HK$197 billion). The firm believes the technology needed to build the structure and to sustain life below the surface of the ocean will be ready in as little as 15 years' time.

"This is a real goal, not a pipe dream," Shimizu spokesman Hideo Imamura said. "The Astro Boy cartoon character had a mobile phone long before they were actually invented - in the same way, the technology and know-how we need for this project will become available."