China has had a few years to be prepared for such things and has an idea of what can happen based on Ukraine so they do have a few different approaches, like seting a red line and nuking the US immediately after it's crossed or what I think is more likely, do nothing in regards to this intrusion other than station boats between the yankees and China while increasing decolonization efforts and sending weapons to Yemen and Russia, supporting a possible takeover of Ukraine while trying to push the more trobolesome elements of Ukraine to flee to the EU so they start causing trouble there.

Taking the opportunity of the colonialists probably not accepting the UNSC cease fire proposal to sanction them and key western industries related to them with the BRICS and Global South, increasing the cost of genocide to the whole west could also be a good move. And although I don't expect China going against the west in a more direct way diplomatically this could be the time for them to get maximum return on whatever they do, specially if they are already going to be blamed for it one way or another.