There's more than two. New York has about ~8 million pop. From the top of my head I can at least tell you that Shenzhen, Guangzhou, and Chongqing have over 10 million residents but there's probably more.
I think you may have pulled up NYC's metro area population and compared it to the urban population of Chinese cities. The metro population of large Chinese cities is in the 20-40 million.
It's kind of a question of where you draw the boundaries. Chongqing counts ~30M because its administrative area is the size of Austria. The UN World Urbanization Prospects project [0] tries to establish comparability between nations, and came up with a top 10 of:
1. Tokyo - 37M
2. Delhi - 29M
3. Shanghai - 26M
4. São Paulo - 22M
5. Mexico City - 22M
6. Cairo - 20M
7. Mumbai - 20M
8. Beijing - 20M
9. Dhaka - 20M
10. Osaka - 19M
NYC is next at #11 with 19M.
However, if you count strictly by "city proper" (as defined by a very wide range of administrative agglomerations), there are indeed THIRTEEN cities in China larger than NYC. I'm not sure this is a hugely useful metric, however, as economically-relevant city boundaries aren't truly represented by administrative lines of control.
Metro area population is a better comparison though because city political boundaries are arbitrary and vary greatly city to city and country to country. The political boundaries in the US are much older than in China, for example, so they correspond a lot less well to where population centers actually ended up being, especially post-automobile when suburbanization allowed people to easily live outside the existing boundaries of a city's limit. And then, crucially, the city's limit was then never redrawn to accurately reflect all the people actually making up a part of that city's economy. Pull up a map of China from 1930 and it's completely different from today, whereas a map of the Northeast US from 1930 is nigh indistinguishable from today.
