Consecutive visa free city trips?

How about this scenario?

I travel from Singapore to Guangzhou (no longer than 72 hours) , then to Beijing (no longer than 72 hours), then to Shanghai (no longer than 72 hours), then to another country eg Japan/Korea/Hong Kong. Each trip will be to and from the appointed allowed airport, no trains/car/alternative modes of transport.

Is it allowed to do mulitple consecutive free city transits?