I came across a video on Youtube discussing it (there are several), and Kowloon Walled City is just endlessly fascinating. A few notable videos I found on the subject were:
Kowloon Walled City: Hong Kong’s City of Darkness
Inside Hong Kong’s Kowloon Walled City
There is also a book on the city called City Of Darkness Life In Kowloon Walled City, which I found on archive.org in high resolution. It is full of photographs and detailed accounts of the comings and goings within the enclave.
The Chinese government never actually had any authority there. It was completely within Hong Kong, and the British didn’t let them go there.