You don't even have to go all the way to China. The English countryside has multiple so called "accents" that are basically unintelligible to a speaker of London English, with plenty of famous examples in popular media (e.g. [1][2]).
Similarly, Germany has plenty of mutually unintelligible dialects. They are all related to each other and any two geographically adjacent dialects are mutually intelligible, but as distance grows it becomes harder to bridge the gap (which is why everyone learns Standard German nowadays). Luxembourgish meanwhile is in every sense a dialect of German with French influences, but due to having an army is considered its own language.
Similarly, Germany has plenty of mutually unintelligible dialects. They are all related to each other and any two geographically adjacent dialects are mutually intelligible, but as distance grows it becomes harder to bridge the gap (which is why everyone learns Standard German nowadays). Luxembourgish meanwhile is in every sense a dialect of German with French influences, but due to having an army is considered its own language.
1: https://youtu.be/Hs-rgvkRfwc
2: https://youtu.be/Z660sool2L4?t=49