Is Hongkong treated as a third, independent region for 144 hour free stay by China

Thank you all for your replies to my previous question. My last question is in order to qualify for 144 hour free stay in Shanghai, for UK citizens flying from Hongkong is Hongkong treated as a third, independent country or is it treated as part of China. Because if it is treated as part of China then different rules may apply and if treated as a third country then there should be no problem for 144 hours free stay. I would be grateful if you can tell me where to find it in writing.
Thank you
kulwant johal