As many as 280,000 families could be living in subdivided flats in old buildings across the city, with many paying higher than average rents, according to a new study by a concern group.
The figure is much higher than the government's estimate last year that 30,000 families live in subdivided accommodation.
The high number was calculated by the Platform Concerning Subdivided Flats and Relevant Issues in Hong Kong, a group formed in March by academics and social workers.
In October and November, the group sent more than 200 college students to inspect 4,045 flats in buildings older than 30 years in six districts, including Western, Kwun Tong, Sham Shui Po and Tai Kok Tsui.
It found that 42 per cent, or 1,639, were subdivided into as many as 10 rooms. The average was 4.3 units.
Using that percentage, the group deduced that there could be 280,000 subdivided units in the 16,000 old Hong Kong buildings - a conservative estimate according to educator Lai Kin-kwok, because the group assumed each block has only 10 flats.
They also found the monthly rent for some of these flats was HK$27 per square foot in October, higher than the average HK$22.20 for 85 private housing developments recorded by Centaline Property that month.
"Many residents we interviewed complained of rising rents and many of them have been waiting for public housing for more than three years," said Lai, from the Caritas Institute of Higher Education.
The group urged the government to impose rent controls and subsidise those residents forced to stay in these units while waiting for public housing.
Officials have no comprehensive statistics on the number of subdivided flats, which are seen as a fire hazard. A survey by the Buildings Department has yet to be completed.
The group's surveyors interviewed 465 people from the 4,045 households.
One of them, Ah Lan, lives with her husband and two sons in a Tai Kok Tsui unit. She complained that their landlord was going to raise the rent by HK$2,000 to HK$5,880 next month. "I don't think I can find accommodation here below HK$4,000. And I don't know when I can get public housing," she said.
Her husband, a decorator, has been on the waiting list for public housing for six years.
They were offered a flat in Kwai Shing in 2009 but rejected it because the location was inconvenient.
The number of applicants for public housing topped 200,000 in September. The government is considering building more than its target of 15,000 flats a year but has dismissed calls for rent controls on private property.