I was in Guangzhou in 1982 as a tourist up from HK. I recall visiting a commune, a farming community with its own medical 'hospital' and lone policeman.
And I have distinct memories of having eaten at a restaurant in the city that divided each floor by class system.
Ground level: tables only, no chairs, no table cloths. Rats running around. First floor: tables & chairs with table coverings. very basic. Second floor: what we would today consider a standard restaurant livery Third floor: the most majestic of restaurants I've ever visited.
Back then the population of Guangzhou was 2M. It was a burgeoning fishing village. 40 years later and it has grown to 15M.
If you include Shenzen in that area (a wider metropolis) it's 15M + 13M. A Chinese Mega-city.