With its marble-clad lobby, sweeping balcony views and sleek, modern decor, Donny Chan's apartment building would seem the kind of upscale tower most young Hong Kong professionals aspire to live in.

But not for Chan, 39, who avoids spending time in his 19th-floor apartment because it measures just 18 square metres. His parking space-sized studio in the grandly named High One building is part of a growing trend for so-called micro apartments that are diminutive even by the standards of space-starved and densely built Hong Kong.

“Every time that I step back into this (apartment) I kind of feel like a cat squeezed into a box,” said Chan, an art director at a medical equipment maker. To avoid returning to his cramped and claustrophobic apartment before bedtime he plays basketball or badminton, goes to the movies or karaoke bars, and gets together with friends and family.

“I go walking in shopping malls until the last minute when they close,” he said.

Hong Kong’s property developers are scaling down, way down, for younger, middle-class buyers, offering micro-sized upscale apartments with eye-popping price tags. The apartments, dubbed “mosquito-size units” or “gnat flats” in Chinese, are drawing online ridicule and underscore worries over the Asian financial hub’s overheated real estate market and widening inequality.

Hong Kong is often ranked the world’s costliest housing market.

Its micro-flat boom parallels tiny house and minimalist living trends seen in the US and other developed countries. The difference is that in Hong Kong, few make the choice willingly.

Chan moved in last year after splitting up with his wife. He viewed 20 other apartments over three weeks but they were all more expensive, in worse condition or farther from his job.

When they first appeared, micro-flats were mostly snapped up by investors renting them out for above-average returns. The government has moved to cool such speculation, and most demand now comes from people needing a place to live, said Ingred Cheh, research manager at Jones Lang Lasalle.

Even so, their extravagant prices mean the young buyers who can afford the prison cell or parking lot sized units already are privileged by Hong Kong standards, said Edward Yiu, a lawmaker representing architects and surveyors.

Transaction records show Chan’s landlord bought the unit from developer Henderson Land for about $US500,000 ($A656,400) in 2015. Chan’s rent is $US1300 a month, or a third of his monthly salary.

He said he’d never consider buying such a small place to live. The down payment on a bigger apartment, if he were to buy, would mean “I’ll be saving until the day I die.”

Last year, developer MT Sisters’ AVA 55 project sold units as small as 15.4 square metres for as much as $US500,000. Blueprints showed the builder was eliminating separate shower stalls, including them in the toilets, to save space, an arrangement usually only found in older buildings.

It took decades for the government to provide housing for the city’s hundreds of thousands of refugees from mainland China, and personal living space has always been at a premium. But apartments are indeed shrinking.

Last year, developers built 206 apartments smaller than 20 square metres, up from 79 in 2015 and none in 2012. This year, 30 per cent of the 17,122 apartments set to be completed will be smaller than 40 square metres. That ratio will rise to 43 per cent in 2018.