My impression is that there isn't an open-house demand for Native English Teachers.
From the Public sector, getting a job working with Hong Kong schools depends on fulfilling the necessary requirements: 1. Native English speaker; 2. University Degree 3. TESL training.
And anything else added to this (like experience) helps.
Of course since there are a few exceptions of some schools
scrambling and some people having friends who got snatched up as NETs without needing any of the requirements, it can be easy to get the impression that there is a free-for-all of NET openings out there.
In the private sector, for the most part it's supply and demand, and I've heard about centers hiring a lot, and stop for a while; it ebbs and flows with supply and demand.
But there's another interesting factor: If you are Chinese, overseas-born or not, expect to find it difficult to find a job in the private sector (with a privately-owned center). Hong Kongers like to have a taste of the Western World with their expensive English lessons, and they don't feel they get that from another Chinese. It is difficult in Hong Kong (minus the exceptions of course) for Chinese people to find jobs teaching Chinese. Hey, I don't make the rules, but I know if I want to learn Chinese, I admit I'd prefer my teacher to be Chinese. So sue me.