Getting into a fully-funded PhD program for biomedical sciences or engineering in the US is not difficult, even for international students.
Profs need PhD students and postdocs to perform their experiments or the work doesn’t get done. There are problems with the overproduction of biomedical PhDs, because there are not enough permanent positions to employ them later.
There is a movement within biomedical science to move toward a different model. This model would have fewer PhD students and postdocs doing the daily laboratory work, and would shift toward creating more permanent staff positions for people with PhDs to have stable careers doing work in academic labs.
I fully support this movement, but it is far from the norm right now, and it will take a long time to implement if it even happens. I seriously doubt that there will be any difficulties for the foreseeable future for students applying to biomedical PhD programs in the US. The positions are plentiful, well-funded, and not hard to get.
I can see some advantage to doing your undergrad in the US if you want to do PhD in the US, but I don’t think it’s worth the cost difference if Hong Kong undergrad is cheap. There are TONS of international PhD students here and they don’t have trouble getting into programs.
As for employment after the PhD, I know nothing about academia in Hong Kong. I do not advise you to plan for an academic career as a biomedical PhD in the US. It is brutal and to be totally frank, you’re not likely to find a faculty position. That would be if you do your PhD in something other than engineering, such as: bioinformatics, molecular biology, neuroscience, physiology, biochemistry, etc.
You would be more likely to find a faculty position as a BME professor (as opposed to other biomedicine) in the US, because schools have trouble recruiting engineering professors here. But academics is a rough road and you absolutely need a backup plan. An undergraduate engineering and/or CS degree is a great backup plan, since you can have a stable career right out of college.