China has at least two major problems. 1) It is very unlikely China will be able to gain the local air superiority/air dominance needed for a chance at a successful amphibious assault.
2) They don't have nearly enough amphibious assault vehicles or landing craft to pull it off. What they do have...
Yeah, one city flooding with a foot of water is exactly like half a country experiencing flood after flood after flood. Give it a rest. China is not all that. Never has been under the CCP and never will be.