If you both have permanent residence in Hong Kong, then you probably can adopt from China; otherwise, you must "be examined and approved by a responsible agency of the adopter's resident country". Read Article 21 of the PRC Adoption Law (found here:
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There also may be a problem obtaining a one-way permit for the child to live in HK. All Chinese citizens who move to HK should have this permit and can wait years to get it.
With regard to a Chinese couple having preference over non-Chinese couples, I think you'll find that every country has some sort of priority list. Other considerations are age, whether you have other children, how long you've been married.
We adopted in HK twice. It was quick and painless. From start to bringing them home, less than 9 months for our son and about 4 months for our daughter (his bio sister).