Xing is organizing a rebellion against the Eunuchs and has succeeded.
Zero anticipated that and made a move to do... something.
There a several possibilities. He could be trying to secure India's independence since hints were dropped that they were helping Zero ALOT, probably in hopes that he would return the favor.
Another possibility is that he is taking Tanzi hostage and doublecrossing Xing in order to secure his continued survival. Xing is both smart and talented, and has used the BK's as a tool before (back when they were at the embassy in Japan.) Zero might be doing this to ensure that he has something to bargain with and not be at the mercy of Xing's faction which may or may night simply decide to do nothing other than house them.
Either way, Lelouch has stated that it was his plan all along to gain control of China so that he could use it to bring down Britannia, and it seems that this is going to contribute to that at least in some way.