The Taxi Driver - David Chiang (1975) - Observatory Road, Tsim Sha Tsui

The bad guy's girlfriend (played by Terry Lau) lives in an apartment on Observatory Road. There are very few roads in Kowloon that are this steep so narrowing down the location was a bit more straightforward (I had no clue where this was 10+ years ago when I first covered the film).

The ornate looking building on the corner was the Luna Building. It has previously been featured, very briefly, in The Peking Medallion.