China feared to be hiding missiles in shipping containers

This reminded me of the comedy reddit thread of China using the sea to hide its submarines:

https://www.reddit.com/r/technicallythetruth/comments/ap374i...

One thing I've wondered: how hard would it be to smuggle a nuclear warhead into a foreign city, hide it somewhere and keep it there until you're ready to launch it via automated trebuchet or some other low tech method?