Unlike everywhere else in the world the chinese bronze age appears with a bang, everywhere at once, with no preceding copper age or other technological stepping stones. This strongly suggests the arrival of a bronzeworking culture which dominated the region.
Genetic evidence suggests that the people of northern china (I forget the regaion) used to be much much more closely related to europeans.
Ancient tales about chinese folk heroes often talk of them having blue/green eyes and sometimes even red hair, attributes which simply do not exist in the han population.