When I did a locations thread for this film on Gwulo a while ago, this was by far the most interesting one - mainly because no one knew where it had finally sunk. Anyway, the guys on there got their resourceful hats on, as always and finally nailed it as being a part of the sea off Stonecutters Island that now sits under a bit of reclaimed land.
Of course everyone who has seen the film knows this location served as the covert HQ of Bond's boss in HK but, in reality, it was the old Queen Elizabeth ship that had been bought by the shipping magnate C.Y Tung (the father of HK's first lame duck Chief Executive - Tung Chee Hwa - the first of many I suspect). He bought the ship and was in the process of turning it into a floating university (called the S.S Seawise - C.Y's...geddit?) when it caught fire under mysterious circumstances in January 1972 and was burnt to the rusty hulk you see on film.
The main part of the superstructure that was above water was broken down and (I believe) was used to form some of the ground on which Chek Lap Kok airport now stands whereas the remaining part remained on the seabed until the area known as CT9 was built over it (CT stands for Container Terminal) at the SE tip of Tsing Yi island (the new Stonecutters Bridge virtually passes over the top of the area now).