Frankfurt -> Guangzhou -> Bangkok -> Guangzhou -> Xiamen -> Frankfurt

I will travel Frankfurt to Guangzhou and 3 h later transfer to Bangkok for 2 days.

then return to guangzhou for stay in guangzhou en shenzen for less than 72 h

my flight back leaves from guangzhou first to xiamen then to frankfurt.
the frankfurt -> guangzhou is inbound, guangzhou -> xiamen -> frankfurt outbound legs of one ticket

do i need a visa for my 3 day stay in guangzhou?

i am worried about leg guangzhou to xiamen....