That’s for the theory. When a neighbouring country detects an increase in radioactivity, it is often too late.
China is not known for being the most open country in the world and a regime of transparency. The proof of this is the incident at the Taishan EPR in 2021, where there was a delay in communication and divergences with its partners. China having communicated on a performance problem while there was damage to the fuel rods. The incident also raised questions about safety standards and regulatory practices in China, including the decision to continue operating the reactor despite signs of degradation. Some reports have suggested that Chinese authorities may have considered increasing permissible radiation limits to avoid shutting down the reactor, an allegation denied by China.
We can legitimately question how a major incident would be managed. A Chernobyl-type transparency, some elements of which are still unknown today.