All the major nations have several cities through which the growth has been driven. China has several cities, apart from Beijing and Shanghai, the economies of which are as big as many nations. Hangzhou, the capital of Zhejiang province, is a major bustling city that hosted the G- 20 summit in 2016 while Shenzhen`s story is well known.
There are also negative effects of the agglomeration as once beyond a size the city hubs face issues like overpopulation, congestion, inadequate infrastructure, etc. A typical example is Mumbai which for the past so many years has seen traffic snarls, overpopulation leading to congestion and breakdown of infrastructure in monsoons.