This plant actually is quite common in the mainland part of Hong Kong.
I've seen one reaching a height of about 10m in Nam Chung.
It has often been mistaken as Aralia sp.
But the pinnate cpd leaf is clearly distinguishable from the bipinnate cpd leaf of the latter.
There's abundance of oil glands ( even found at the margin of the leaf ) and the leaf base is slightly oblique.
The nearest match I would say is Zanthoxylum ailanthoides.