Some scenes can even be traced shot for shot with real locations, including unreal Kai Yak airport landing approach over kowloon
It's from this book:
William Gibson visited the city and described it in his 1997 work, Idoru:
"There was a place near an airport, Kowloon, when Hong Kong wasn't China, but there had been a mistake, a long time ago, and that place, very small, many people, it still belonged to China. So there was no law there. An outlaw place. And more and more people crowded in; they built it up, higher. No rules, just building, just people living. Police wouldn't go there. Drugs and whores and gambling. But people living, too. Factories, restaurants. A city. No laws."
The "no laws and/or regulations in KWC" is a bit of a myth though, HK police began patrolling the place in the early 70s, plus despite its legal status it benefited from HK's infrastructure, such as postal services or the electric grid. It was lawless mostly in its number of unlicensed dentists.
But ... it didn't actually work all that well, did it? It was a huge slum, which plenty of cities have. It was just unique in its small urban footprint.
I’m kind of sad to see it gone because it was like having a small version of Blade Runner in our time. But more important, actual humans lived there, and I wouldn’t wish that on anyone.