This is the second of the grave sweeping holidays, together with Ching Ming which is in the spring.
The things you do are basically the same, it is traditionally a day for the family to go and respect their deceased ancestors. When we were young we took this seriously though in my family it is not so much any more.
However if you do go to the graves on that day you will see many people there, it’s a busy time and as well as being a Chinese tradition — and a family tradition for many — it can also be a nice day out. Of course there are sad thoughts too.
Traditional you are supposed to “go up the mountain” on this day. The story goes that a long time ago there appeared a devil of plague in the Ruhe River. A kid named Heng Jing was taught by an old Taoist how to defeat this plague.
The priest told the boy that the devil would come back on the 9th of September and told him to go back and save the village. He did this by telling them to go climb up a mountain, then while the villagers were safe he tricked the plague devil with some strong Chinese wine made of Chrysanthemum flowers and killed him.
As this festival is held in Autumn when it is very dry, well dry for Hong Kong, with humidity below 50% — there is a high risk of hill fires. So this is really bad when people are going to the hill sides to clean graves and offer burnt offerings!
Of course the fire department tells everybody to be careful, and there are special fire-proof bins provided to put burning ash, but even so there are always hillside fires which is a great shame as really Hong Kong has some lovely countryside.