Suzhou is next to Shanghai and you devastate them both with a single nuke. https://en.wikipedia.org/wiki/Suzhou
My guess is an 10MT H-bomb could kill ~20 million people by aiming at Suzhou despite the city only having 6.7 million people. Honestly to cripple China with minimal nukes 2-3 Starfish Prime style Nuclear electromagnetic pulses could disable most of their east coast before you target individual cities.
Also, responding in kind to a limited nuclear exchange may be appropriate if you think an adversary still has a large stockpile. There is a lot of uncertainty involved.
Nukemap, known to lots of people here, can help you explore your predictions. Here, I airburst a B-83 over Shanghai so you don't have to: https://nuclearsecrecy.com/nukemap/?&kt=1200&lat=31.2322758&...
Sleep tight...
Hard to say what hypothetical countries arsenals actually look like. The B-41 was supposedly 5.2 megatons of TNT per tonne of bomb designed in the late 1950’s. At 5 tons each a non reusable falcon 9 could get ~4 different 25 Mt bombs to LEO and possibly more on a ballistic trajectory. So it’s not like monsters don’t fit on rockets, saturation bombing is just more effective.
My point was just that the logic of having only a few nukes while everyone else has many more doesn't work. China has 145 cities that have more than 1 million people. You wouldn't be a serious threat to their industrial base with only a few nukes, and so the effect of your deterrence would be minimal.