Seasteaders are fantastic. They’re toddler billionaires, grumpy and fed up and not going to put up with pesky guv’mint any more, running away to the bottom of the garden – sorry, I mean international waters – to start their own country. It’s a grand idea, until it rains, or there’s a hurricane, or a medical disaster, or pirates, or dinner time.

Yet it would be churlish to dismiss floating cities out of hand, because as an idea it probably has merit in other ways – for instance, as an extension of a city that’s already too crowded, with land that’s too expensive, but where there is real demand for new facilities. In that vein, architecture firm AT Design Office has produced some renders of a part-floating, part-underwater city for Hong Kong called (wait for it) “Floating City”.

Look at this damn thing, though:

AT Design Office created these renderings on commission from China Communications Construction Company (CCCC), with a very specific brief: to use the same prefabricated technology that has been used in the construction of the Hong Kong–Zhuhai–Macau Bridge, which is due to be finished next year and connect the three major cities of the Pearl River Delta. It’s 50km long, and its tunnels and elevated sections are made using prefabricated concrete sections to speed up construction time and lower costs. Floating City, as a concept, is meant to show the flexibility of prefab parts – so not only can you make a boring bit of highway, you can also create a 10km2 floating city with parks and malls and all kinds of stuff.

The most prominent example of prefab’s Chinese resurgence comes from the Broad Group, an air-conditionar manufacturer that branched out into construction by applying lessons from its factory lines to architecture. Its buildings exciting only because of how fast they’re built – in one timelapse video, it’s possible to watch a 30-storey building goes up in just 15 days. In 2012, Broad announced that it intended on building the tallest building in the world, the 220-storey, 838m Sky City, in Hunan Province, and it would do so in only 90 days. Despite breaking ground on the project in July 2013, construction has yet to start due to a series of issues with permits and environmental assessments.

Sceptics argue that prefab buildings like Sky City can lack architectural merit because of how inflexible they are. As the savings come from manufacturing lots and lots of the same piece over and over again (like in traditional mass manufacturing) it means that there is little room for flair or character – Broad’s buildings are square, dull things, somehow managing to appear squat despite their size.

That makes AT Design Office’s renderings all the more impressive, if they’re indeed based on using prefab units as claimed. Here’s AT Design Office’s blurb:

“The basic construction unit is a prefabricated block – 150 metres length and and 30 metres in section. On plan, the grid can be an equilateral triangle and a pentagon. The prefabricated parts can be overlapped vertically. During construction, the modular parts are floated to the site after pre-fabrication in the factory.

“The floating city has a perfect internal and external traffic system, linking it within but also with the outside world. A cruise dock serves giant ships, a yacht dock serves private vessels and civilian submarine traffic. Submarines and electric vehicles are the main means of transport on the island – keeping the island free from air pollution and congestion caused by automobiles. The main traffic flows are facilitated via the water canals above and below the water surface. The peri-urban area house farm, hatchery and garbage recycling centre.”

There’s grass everywhere, and ventilation comes from massive chimneys. An underwater hotel and “entertainment city” would draw in the tourists, and energy production would come from tidal power. It would provide “world-class facilities” that meet the needs of a growing population without taking up any valuable farmland. It’s almost more like a floating archipelago, an artificial Venice, with tunnels and bridges connecting manmade islands as people travel around in private yachts and on public river taxis.

That all said, there is little chance that Floating City – as it appears here – will ever be built. According to Dezeen (which has a gallery of more images of Floating City and an interview with architect Slavomir Siska), the China Transport Investment Company is assessing whether to start building a small-scale version next year, with the implication that Hong Kong would be an ideal site. However, a 10km2 floating city with unsealable underwater chambers, as home to possibly thousands of people, sounds like one natural disaster away from a Roland Emmerich movie. These types of speculative ideas are better thought of as the haute couture of architecture: radical, unrealistic, but also thought-provoking and possibly trendsetting, like when Kanye put models in leather jogging pants.