More than 170,000 people in Hong Kong are living in cramped subdivided flats, a government-commissioned study has found, underlining the scale of the city's housing crisis.

Tens of thousands of low-income families and immigrants are forced to live in the tiny subdivided units, unable to afford sky-high rents in the crowded city of seven million.

Hong Kong's Beijing-backed leader Leung Chun-ying has promised to make tackling the housing problem a "top priority" by boosting the number of new homes for Hong Kong people.

But the study showed the problem is even greater than previously thought, with an estimated 171,300 people living in 66,900 subdivided flats.

"About 30,600 such units do not have essential facilities such as kitchen facilities, independent toilet and water supply," Secretary for Transport and Housing Anthony Cheung told reporters late Monday.

The study was carried out from January to April by Policy21, a survey organisation comprising academics from the University of Hong Kong.

The Census and Statistics Department last October estimated 64,900 people live in subdivided flats, cubicles, caged bed spaces and cocklofts, which are usually around 40 square feet (3.72 square metres).

The smallest of these cubicles cost less than HK$200 ($26) a month. But poor workmanship and lax standards in subdivided apartments often create structural dangers, hygiene problems and fire hazards.

In 2011 a fire which started in a street market killed nine people from a nearby tenement after they became trapped as they tried to escape cubicle-style flats through a maze of narrow hallways.

Many of the victims died of suspected smoke inhalation in a stairwell that appeared to have been blocked.

The Asian financial centre has some of the highest property prices in the world, driven by limited supply and speculation from wealthy mainland Chinese investors.

The government has raised real-estate purchasing and resale costs for non-local buyers in an attempt to cool the overheating market.