I imagine pretty easily. They likely don’t have to find it, nothing gets dug in North Korea without US watching it via satellite. Chinas air defenses likely don’t exist in North Korea.

I have no doubt the US has plans to cut them (and probably anyone else you can imagine) off in the event of war.

Apparently China's navy is stronger than the US navy these days.

So it might not be a great idea to start doing stuff like that in their back yard? ;)