The wealth gap divides not only individuals and families but also parts of the city, with a family in the richest district earning three times as much as one in the poorest.
Wong Tai Sin was the poorest area last year, with average family income of HK$19,300 a month, up HK$500 from a year earlier. Central and Western, meanwhile, overtook Wan Chai to become the richest with HK$60,800 a month, up HK$11,600.
Professor Paul Yip Siu-fai, of the University of Hong Kong's department of social work and social administration, was not surprised.
'It is normal that low-income families aggregate in several districts. That is Hong Kong. There is also a large variation in income even within the same district,' he said.
Property agents said the surge in household income for residents in Central and Western was due to construction of the MTR West Island Line, expected by 2014.
Anthony Wong Ka-lam, a senior sales manager with Hong Kong Property Services, said there were 40 per cent fewer housing vacancies in Central and Western last year than in 2009 as better-off people moved in to take advantage of the new line.
'Those who move into the Western district are usually middle-class families with children. The transport will be more convenient and it is known as a district with elite schools,' he said.