Have you any idea how many ships the Chinese would have to assemble for such an invasion?
D-Day in 1944 assembled just short of 7,000 ships, including landing ships. And that was just to cross the English channel!
China would probably have to assemble a similar number, as even though the ships are much larger today, and would have greater holds to carry all the necessary war materiel, they wouldn’t have a ready source of re-supply just 100 miles away (it was about 100 miles from the English coast to Normandy). Thus, they’d have to carry pretty much everything they’d need for a long campaign. And they are not going to achieve air superiority.
We’d know all about their intentions before they ever weighed anchor. It would be obvious it was an invasion force. Once the armada got into the Philippine Sea it would be obvious the target would be either the US or, if it turned south, Australia. In any event it would be war, and the initial engagements would take place in the Philippine Sea, no matter what the target was.
The Pearl-Harbor style nuke-attack on USN would happen first.
The shipping would be normal shipping - just surprise-filled with ChiCom soldiers. The first you learn of it would be: the nukes struck most USN Pacific ships, and the door swung open on the shipping container at 5000 locations up and down the west coast. It will be a complete surprise attack, not a telegraphed attack-flotilla.
After we attack in your scenario, China simply announces it was an exercise. No invasion. Now what? We just attacked a nation who was only conducting an exercise.
China has 6600+ in its merchant marine.
It’s enough to do it, if preceded by a big surpise
west coast & USN nuke strike.