There are about 10,000 alive today
There was a mixing of the Chinese (Han) and these people thousands of years ago in the Tarim basin. This mixing produced, I believe, the Scythians, Xiongnu and the Hakka. The Hakka migrated all the way across China into south China, Korea and Japan. Their records and legends indicate that during their migration anyone with Caucasian features were executed. (many tried to conceal their appearance)
I also believe that some mixing of all these groups later produced the Huns.( also with possibly an Iranian element.)
An excellent book to read on this subject is The Tarim Mummies by Victor Mair.
"Genetically speaking, some Hakka people have clearly inherited some non-Han features such as wavy hair and high nose bridge."