More than 171,000 people are living in substandard, subdivided flats in Hong Kong, it was claimed yesterday.
The estimate is more than double the total of 64,900 given by the Census and Statistics Department last October.
And the figure is thought to be even higher as researchers could not examine illegal homes in industrial buildings, said the secretary for transport and housing, Professor Anthony Cheung Bing-leung.
The study was commissioned by the government to give a first indication of the scale of the problem.
Cheung said after a meeting of the Long Term Housing Strategy Steering Committee yesterday: "I can't say whether it's a large or small number, or whether there's an increase, because this is the first time we've done it. But as we draw up the housing strategy, we'll take the data into account."
The committee will make its recommendations by August.
The study results coincided with another government release, which said home prices are the least affordable since 1999.
The mortgage-to-income ratio of a 45 square metre home, for a family earning the median income, surged from 52 per cent in the preceding quarter to 56 per cent in the first quarter this year.
And in a further indication of the city's housing woes, it was revealed the number of applicants on the waiting list for public rental accommodation climbed to a 20-year high of 228,400 by the end of March.
The administration has identified the problem of subdivided flats as a priority. Low-income families and new immigrants often choose to dwell in such units, conveniently located in old buildings in the urban centre. But poor workmanship means they create fire risks and a danger of leaks and structural overload.
The estimate of 171,300 is 2.6 times the figure given by the Census and Statistics Department. The study was carried out by Policy 21, a company set up by academics from the University of Hong Kong.
Researchers visited 10 per cent of the city's 18,600 blocks older than 25 years. Blocks of residential or mixed uses were sampled from each of the 18 districts.
They found flats were divided into 3.6 sub-units on average and projected there were 66,900 subdivided homes. Of these, 30,600 lacked their own kitchen, bathroom or water supply.
Committee member Dr Andy Kwan Cheuk-chiu said the government should focus on the 30,600 units in the worst condition. He said: "They should see if people living there are in need of social welfare and relocation, and whether the buildings have a safety problem."
Sze Lai-shan, of the Society for Community Organisation, said the government should reinstate rent control - which Cheung has repeatedly ruled out - and give a rent subsidy to such residents.