News: underwater cities with infrastructure networks spiralling down into the depths of the oceans could be a reality as soon as 2030, according to a Japanese construction company.

The conceptual Ocean Spirals could descend by up to 2.5 miles below the oceans' surface to create self-sustaining underwater communities that could be home to up to 5,000 people each, says Shimizu Corp.

The helical structures would be made up of resin components, produced using huge industrial 3D printers.

Each one would be topped by a watertight floating dome containing businesses, homes and hotels, which would submerge underwater during bad weather conditions.

Beneath this, the nine-mile-long spiral would wind its way down to the seabed to allow scientists to create an "earth factory" of natural resources that could be harvested for energy and materials.

According to the Tokyo-based company, micro-organisms could be used to turn carbon-dioxide into methane.

This would fuel power generators along the spiral, which would also take advantage of differences in seawater temperature to create additional energy.

Hydraulic pressure would be used to produce desalinated drinking water.

Shimizu – whose other projects include a space hotel and a floating city –  predicts that the first spiral will take five years to build at an estimated cost of ¥3 trillion (£16 billion). The company says the technology to sustain underwater life will be ready in 15 years, meaning residents could move in as early as 2030.

The concept was developed in partnership with Tokyo University and the Japan Agency for Marine-Earth Science and Technology (Jamstec).