The Triads' rule lasted up until the mid-1970s, when a 1973-1974 series of over 3,000 police raids occurred in Kowloon Walled City. With the Triads' power diminished, a strange sort of synergy blossomed, and the Walled City began to grow almost organically. Square buildings folded up into one another as thousands of modifications were made, virtually none by architects or engineers, until hundreds of square metres were simply a kind of patchwork monolith. Labyrinthine corridors ran through the monolith, some of those being former streets (at the ground level, and often clogged up with trash), and some of those running through upper floors, practically between buildings. The only rules of construction were twofold: electricity had to be provided to avoid fire, and the buildings could be no more than about fourteen storeys high (because of the nearby airport). A mere eight municipal pipes somehow provided water to the entire structure (although more could have come from wells). By the early 1980s, Kowloon Walled City had an estimated population of 35,000 - with a crime rate far below the Hong Kong average, despite the notable lack of any real law enforcement.
Over time, both the British and the Chinese governments found this massive, anarchic city to be a bit too much - despite the low crime. If the 'Black Market' ever had a physical location, this would have been it. Needless to say, the sanitary conditions were, well, a bit wanting.
After the Joint Declaration in 1984, China allowed British authorities to demolish the City and resettle its inhabitants. The mutual decision to tear down the walled city was made in 1987.
At that time, it had 50,000 inhabitants on 0.026 km², and therefore a very high population density of 1,900,000 / km². It was allegedly the most densely populated spot on Earth.

that's equivalent to 2.2billion people in singapore!!
