All About Ah Long - Chow Yun Fat (1989) - Yuen Long Industrial Estate, Yuen Long

At various points in the film we see an area where the motorbikes are practising. The first time is when Ah Long goes to see his friend, played by Ng Man Tat. In the initial scenes the area is a bit non-descript but it pops up again later in the film with a large clue to its location in the background. The first two images below are from the first time we see the area in the film but the bottom image is from later on in the movie (you can tell because Chow Yun Fat has had a hair cut). Note the building just behind Chow's head. It looks like an old house with a belvedere on the roof.

There are a few old buildings like this in Hong Kong (Jessville for example, but there used to be many more), but this one looks suspiciously like the Yu Yuen mansion in Yuen Long. Low-and-behold, in the background are some industrial buildings that (some) still stand along Wang Yip Street West in Yuen Long. This means it is Yu Yuen and the location where the bike track is located is the Yuen Long Industrial Estate - before it was constructed. It looks like the bikes were doing a circuit of Wang Lee and Wang Lok Streets because they did exist in 1989, even though the estate buildings had yet to be constructed.

Yu Yuen is still standing as far as I know, but how long it will be there is anyone's guess. Most of these old grand mansions in the New Territories have long since been redeveloped.