Ask Lemmygrad

Eh they have the island chains which help a lot. I'm not saying they can strangle them like Cuba and stop everything in and out. I'm saying they can make it uneconomical, painful, expensive, economically hard on China by trying to intercept most boats. They can't stop China from running some small boats, speed boats, etc or doing stuff over land but they can stop the big cargo ships which make up the bulk of Chinese trade and shipping, those are easy to spot using satellites and drone fleets and can be tracked out from port.

China would likely intervene against this which is why I think the US is planning on using autonomous robot death drones IF and I repeat IF they actually want to go the physical blockade route (economic may be all they try). Basically advanced sea-faring, self-propelled mines. Their special forces top leadership have talked of creating such a minefield to deny the PRC Taiwan in a battle and buy time to land US forces, I think though they'd try and use traditional naval ships to enforce it that their plan is as soon as those start getting sunk they get the angry public behind creating masses of kind of AI or autonomous/semi-autonomous self-propelled and seeking drones and just litter international waterways that access China with them.

I'm not saying the plan would work but it would escalate things in the way they want towards the ends they want which is buying time, driving up anger at China and trying to make things painful and costly and a drag on them. And more importantly towards making China hit them, they've been trying to get China to strike them, to give them an excuse, etc for some time and the Chinese keep ducking it and proceeding calmly with the plan. So if their plan is to use "rules based order cordon" around China and China uses military force to disrupt it then they've succeeded in their long-time goal there of getting to claim their actions are merely retaliation for "aggression".

The bigger issue is still US sanctions. Once they slap those on a lot of countries significantly reduce trade with China because they refuse to confront the US or make an enemy of them because whoever does that first gets the US navy and marines in their face to make an example of them and no one wants to go first. If not the direct force then at least devastating sanctions against industry that torpedo a given country's economy.