Licson Lee says to YSITD
Although Hong Kong’s population density is lower than Singapore’s, it is in fact way higher if you consider that only 23.7% of its land is developed given the mountainous terrain and other factors. Of this, only 76 sq km of land, or 6.8% of the total land area, is developed for residential purposes. An expert estimates that population densities measured at block level in some areas may even exceed 400,000 persons per sq km.