How low was the Hong Kong Kai Tak landing approach over the city?
As the wikipedia article for Kai Tak, Runway 13 approach states:  


  Typically the plane would enter the final right turn at a height of about 650 feet (200 m) and exit it at a height of 140 feet (43 m) to line up with the runway.  


Given that some of those buildings underneath the flightpath were 6-storey and therefore ~60-70ft tall, the aircraft were less than 100ft above the highest rooftops. (This I can personally vouch for, since my sister did for a while live in one of those 6-storey apartment buildings and I have stood on the rooftop watching the planes pass over!)