I don't know how things work in China, frankly, but a general response is:
The "pros" are that you might be able to shorten your time to tenure in such a situation, depending on your current qualifications and how you negotiate. Restarting the tenure clock would, on the other hand, be a "con". Another possible "pro" is if there are a few people there that are known to you that would be worth working with.
There are many possible "cons", however. You should try to get some idea, during any application process, of the long term commitment and funding for the new department.
But, I think the biggest issue, as I mentioned in a comment, is how the department was formed and who the current members are. In the case of a department split off from another or using faculty "contributed" from several departments, it is possible that the faculty in the new department were the "dead wood" from their original departments. I've seen this happen and it took years for the new department to gain much of a reputation, though it eventually did. The problem was caused by the method of creation, in which department heads were asked to "contribute" faculty. The ones contributed were either poor performers or headaches for the department head. Had it been done otherwise, more rationally, the outcome might have been quite different. But a search on the qualifications of existing members might give you an idea of the overall nature of a new department. This worries me more about your first example.
If a new department is created through a hiring "blitz" with a prominent academic selected as head, it might be different. Faculty from other departments might apply and be selected, but they aren't just "dumped" into the new organization.
I'd also think that a "new" department might be more reliable if it had been around a bit longer, letting things settle down, but also starting to establish a reputation. Again, a search on the qualifications of the faculty can tell you a bit about whether they work effectively and, perhaps, collaboratively. This suggests that your second example might be a bit "safer", though not necessarily.
As a grad student I was in a large department that had several factions. Overall they didn't get along very well, but within each "faction" they were very effective and productive.
As for applying to both departments, I see no reason not to do so, especially if you are well qualified for both.
Note that much of the above is just projection of "expected in general" tendencies. Little of it necessarily relates to your particular situation, so you need to take care and do some research.
But, explore early tenure and get a sense of how it would be to work within any department you might consider joining.
