I wouldn't say they are indistinguishable, definite overlap on individuals where you can't tell for certain, but on the average I'd say they are pretty distinct, Koreans and Japanese people being more similar to each other than they are to the Chinese. I would even say northern Chinese (where they speak Mandarin) are distinguishable from southern, and that isn't even counting all the Chinese hill tribes and such.
I wouldn't say they are indistinguishable, definite overlap on individuals where you can't tell for certain, but on the average I'd say they are pretty distinct, Koreans and Japanese people being more similar to each other than they are to the Chinese. I would even say northern Chinese (where they speak Mandarin) are distinguishable from southern, and that isn't even counting all the Chinese hill tribes and such.