Which cities are currently empty? China has 160 cities with over a million people. The US has 10. They seem to be doing a good at getting people there.
http://www.cnn.com/2012/01/20/world/asia/china-florcruz-urba...
http://www.cnn.com/2012/01/20/world/asia/china-florcruz-urba...
We have 50 MSAs with 1 million+:
https://en.wikipedia.org/wiki/List_of_Metropolitan_Statistic...
I think they aren't the right comparison either but quite a few cities are at the center of a larger built up area.
http://www.businessinsider.com/these-chinese-cities-are-ghos...
http://www.forbes.com/sites/wadeshepard/2016/04/23/chinas-la...
Sounds like they build them first then move in the people. Probably cheaper and faster that way? They do have 1.3 billion people.