Japanese designers are preparing for rising sea levels - by making plans for a huge floating city.

Developers N-Ark - who see the idea as the ocean-based version of Elon Musk's SpaceX - say Dogen City would provide a self-sufficient habitat for 40,000 residents.

They explain a new economic zone call New Ocean would be resilient to climate change.

Measuring 4 km in circumference, the plan would be for inhabitants to be able to get to any point in the zone within an hour.

A range of buildings, including a sports stadium, is proposed, and properties are able to be moved by sailing them to another location.

The infrastructure is circular in design to protect it from severe weather and consists of three infrastructure types.

These are a habitable ring containing the main habitable zones, an undersea data centre and medical research facilities, and flexible inner ring structures that can move freely in the inner bay.

N-Ark's development roadmap currently earmarks the year 2030 for completion.

They explain: "New Ocean is a term intended for the ocean version of the private space business innovation "New Space" started by Space X.

"We will propose six elements (medical, food, housing, information, and electrical services) to realise New Ocean, promote the entry of various companies, and promote ocean development activities.

"Through this, we aim to create maritime innovation, and seek to create this future together with participating companies, governments, and universities."