As I write the overnight rate is over sixty-six percent (yikes, although the frequency of reporting that figure is unclear). Hibor, by the way, is the Hong Kong Interbank Offer Rate.
Why so high? The most natural interpretation is that many traders are shorting the renminbi, and in response the Chinese central bank is trying to crush them. There is a short squeeze, and the high overnight rate reflects the need to make good on contracts now.
More generally, it seems both the central bank (PBOC) and the big Chinese banks are buying up yuan like crazy, especially offshore yuan. There is a free (but PBOC-influenced) Hong Kong rate, and the controlled rate internal to China. The freely traded offshore yuan have been cheaper, although about a day ago the two rates converged. The PBOC wants to keep the currency value relatively high, to limit capital flight and to maintain credibility.
In other words, an epic battle is going on. Round one (or is this round three)? goes to PBOC.